Ok so your group has just got together and is heading for the attic to clear out some bats when you stumble across and old mirror... In the mirror they see themselves however they all are doing different things in the mirror than out of it... One presses her hand against the mirror and apparently falls in... they go after her and they all get sucked into a long corridor leading in whatever directions you fancy... Ok if you look in the Manual of Planes (if you dont have access to that book I can explain more) you see a variant plane called the plane of mirrors... What is cool about this plane is that there are no threats except for duplicates of the PC's (which might be a very harrowing threat).. so if they go in at level 1 the duplicates (the only creatures in the place) will be lv 1 too (there are other creatures called Nerra's that inhabit the plane but they dont need to be in this slice, they appear in Fiend Folio)... also this could be their very first planar adventure (very cool although maybe you dont want to pull out the planar guns just yet so maybe save an adventure like this for later)... Now since you need magic to enter the plane of mirror the adventure hook could revolve around finding an old wizard that has been trapped in this plane for awhile (he cast a spell on the mirror to enable the PC's to enter, the house they are clearing out could even be his or something)... after they deafeat themselves they can find the wizard and go home... It could be fun but maybe hard as well since a group of yourselves isnt easy...
This is somewhat more traditional but... your PC's are heading through soem hamlet and they decide to rest there... The next day a small group of orcs or gnolls (or whatever cave dwelling creature of appropriate CR you fancy) attack the village... Many of the best warriors are out for the annual elephant hunt (or a more exotic creature hunt)... so rather defensless your group of PC's save the day.. the leader then explains to you that a group of orcs (or whatever) has been harassing the village for awhile and emplores you to help them... if they agree when they get to the cave a makeshift door automatically shuts and there is a chance that a wind puts out their lights (or not if you dont want to make it too hard)... really the leader is a low-level arisocrat1/dread necromancer (Heroes or Horror)1 or just aristocrat1/cleric1 that has befriended (although not necessarily commands) a ghoul and some zombies or skeletons and has been sending people into the caves to feed them (also he has promised a band of orcs some wealth if they attack the village, this spurred the leader "send" some of its village member to the cave to investigate, and now the tactic has been used on the PC's; really he is planning on sending the orcs into the cave themselves saying it is a family treasure keep or something)... The reason the leader is doing this is because he is simply crazy and because he wants to spawn more and more ghouls since if a humanoid is killed by a ghoul raises as a ghoul)... So teh PC's deafeat the ghoul find a switch inside the cave that opens the door and the encouter is done... you can make this adventure harder or easier by just adding more ghouls (mayeb a ghast or something stronger) and you can expand it by now destroying the leader of the village or something (which may be hard due to the loyalty of the townmembers but if you can convince the townsmembers then...)
Ok you come to a new town and an official asks you to escort a caravan to another town... while doing so the PC's are attacked by a group of humanoids much stronger than themselves... the net them, entangle them, and do subdual damage to the PC's... the PC's all get knocked out and taken to the towns prioson saying that they have been charged with robbery, treason (or whatever you can think of)... Now you can RP a trial if you want... you can make it like a skill challenge... if they win they get exp. if they lose the adventure continues... depending on their sentence they could get broken out by the person who hired them for the escorting job OR you can just have that person break them out without a trial... He tells them that this town is an outlet of a nerby village and that this nearby village has been plagued with bad crops and hunger... but the leaders of the town whom arrested the PC's fear of a plague in the nearby village and will not send supplies... So the stranger who hired you had to act by stealing supplies but he didnt want to risk getting caught himself (nice guy huh

)... you can go multiple ways with this adventure... the nearby village could be plagued and the city people could all be turning cannibalistic , maybe many are dieing and raising as ghouls spontaneoulsy (its said that humans with a taste of flesh rise as ghouls) and maybe the guy who hired you wanted to get more prey to his town... Maybe the leader of the town who imprisoned you are acgually corrupt and you may decide to help out the nearby village by stealing from the bigger town... This adventure has the potential to be ALOT of RP so if you are not comfortable with alot of RP dont do this adventure (also in this adventure you may want to give out story rewards not just combat awards)... Maybe there really is NO town and that guy is trying to manipulate the PC's somehow (maybe he really just doesnt want to get caught stealing but hes not a neccessarily bad guy)... depending on the demeanor of the PC's they could turn the guy who hired them in and clear their names (heck maybe they cleared their names along time ago at the trial)..
maybe they got away from the attackers at the very beginning... if so the adventure could revolve around finding the guy who hired them and figuring out what the heck...
your PC's are walking through a forest going up a mountain and your PC's come across a river... deciding that it was more refreshing and easier to follow the river up they decide to walk up the river (or just give them clues or a road that follows the river, maybe they hear a sound, etc)... they eventually come to a waterfall and a nice swimming hole... Now this a seed for many adventures... maybe there is a cave behind the waterall your PC's hear all sorts of noises coming from behind the cave... if they investigate they see as myrmling green dragon in a tussle with a wyrmling bronze dragon they can decide to help the bronze dragon out (this may be dangerous since the dragon is pretty powerful but with the bronzes help it is definetely possible, maybe it would be fair to say the green just used its breath adn rolled a 4 so it cant use it again for another 4 rounds, and why would the green get an AOO to attack weaker creatures when it knows the bronze will just continue attacking, I mean I dont think a bronze would ditch a group of adventurers that are helping it, just rule it doesnt anyway; maybe you can say that both dragons have a certain # of HP missing or something maybe simulate a fight, or just say that the bronze is doing better and have the green with lower HP than the bronze)...
Maybe there is a lv1 bard [lv2 maybe] that is behind the waterfall cave and that uses silent image to portray a drowning person, if they try to help the person the bard then shoots at them in the water with a bow or something (Im sure swimming instills some penalty to AC or something; i would say they lose DEX bonus to AC and/or they get -2 to AC for an advantageous situation modifier)... If they see through the illsuion and leave them, the bard trys to follow them Hide and/or in conjuntion try to fascinate them... this setup give the bard an advantage but it isnt unwinnable (say it takes DC 10-15 climb DC maybe 12 [10 for being a surface with ledges, +2 for being slippery], and the water fall is light so it gives only concealment (not total concealment) and no cover [you could say the waterfall give cover since it distorts projectiles thrown through but maybe it is only cover against projectiles, which is the only thing the are going to be hitting them with anyway, besides spells which have the 20% miss chance but since you have line of sight an area spell will work fine, although a level 1 area spell is rare; OR instead of cover you can give -2 to attack rolls made through the waterfall because of an advantageous position modifier (not as steep as cover but still helpful)).. this could be a fun encounter and you can modify the power level very easy..