The ideas already stated are good ones - I am just adding to them.
It really does come down to the type of character you want. But just some random ramblings ...
Ranger/Rogue - (and, yes, please don't just take one level of the damn ranger
) Why?
*You maintain class-access to stealth and scouting skills
*higher BAB & HD than straight rogue
*Compared to straight rogue, however, you loose increased sneak attack damage and access to those skills like Use Magic Device
*If the group does not have a wilderness person yet (a druid or a ranger or another class but focus in those woodsy skills) your access to Wilderness Lore, Track, and such would be a great boon to your group's overland traveling
Bard / Rogue - great people skills for when you aren't sneak-attacking them
continued access to skills like Use Magic Device and ability to cast some spells (like invisibility i believe is on the bard list ? but i could be wrong about that - but other spells in general like cure light wounds could be nice
and spontaneous casting is always a boon
Fighter / Rogue - if you are a real sneak-attack kind of guy, or find yourself in the thick of battle more often than you care to admit, go this route. Using some combat feats related to your attacks / defenses of choice could make you a formidable opponent. In essense you would be an assasian without the assassain PrC
Wiz (specialist) / Rogue - Instead of just thinking in terms of a wizard rogue, think of a particular specialist / rogue. Perhaps a Diviner / Rogue - then you'd be like an archeologist or something (of course, you could retain that title with bard instead). Illusionist / Rogue seems a little painful for your enemies but at the same time that may be too predictable.
Other option? Stay as a rogue just don't choose such sterotypical rogue things - for instance, with your feats go in the direction of feats related to knowledge or simply taking skill focus in skills that are cross-class. Or, maybe even using that ABUNDANCE of skill points given to rogues and spend them on skills other than the sterotypical ones (search/disable device/etc). Some cross-class skills...
wilderness lore would make you more proficienct in overland travel and could help if you picked up the track feat
Profession (Sailor) - get some ranks in this and be a boater; perhaps all your adventuring is to save up money to get your own boat?
okay, a little corny and probably not a good idea if your DM doesn't generally go off in these directions... but it's an idea none the less
must stop now as I am just rambling - lack of sleep i guess
But the point in this is to say even if you don't actually take a different class, you can still mix things up by not taking what is stereotypcailly expected of a rogue.
Oh, if you do multi-class, watch out for multi-class XP penalties.. you said you were 3rd so you might run into some trouble if rogue (or your other chosen class) isn't a favored class for your race.