IIRC, the weapons used by characters as our game just ended at 12th level were:
+1 Holy Mace* (Cleric)
+1 Holy, Flaming Bastard Sword* (paladin)
+2 Keen Rapier* (fighter rogue, main fighter)
+3 Undead Bane Dagger and +1 Keen Pick (ranger, undead hunter)
+1 Spellstoring Dagger (sorceress, she was using the undead bane dagger until our ranger traded for it.)
+1 Frostburst Greataxe (barbarian, this weapon sucked)
+1 Quarterstaff (wizard, the same weapon he started with. He used it less than 5 times)
*: weapons that were enchanted or modified in some way by the party.
Our group used Greater Magic Weapon extensively. My character even used an item to boost caster level to buff weapons up to +5. This tactic made us marvelously effective fully buffed, as our fighters were swinging at least +6 weapons. However, first major battle we had without major buffs didn't go so well. Most people couldn't hurt the Death Slaad except with their bonus damage, and his resistences usually took care of that.
Also, these were the weapons we had through 11th level mostly. It's possible that, upon gaining 12th level and the treasure, we would have used our loot to do more upgrades to weapons. However, IIRC, the wizard's player and I had discussed spell storing ioun stones, better cloaks of resistence, and maybe some see invis stuff.
I wouldn't reccomend going above +4 equivalent, because it takes too much money. Rather than getting one awesome weapon, spend some gold on armor, defenses, and most importantly other stuff.
Get around a +3 weapon, spend lots of gold on other things. You want to be able to Fly and See Invisible without help, and probably haste yourself as well. An Ioun Stone of Spell storing (12k) is one of the best buys a fighter with some friendly casters can have.