Lessee, in V3 and 3.5;
1> Really cool Mobile Fighter idea that I got to play up to 4th level in a 3.0 game. Really shined vs the mooks we were always fighting. Nine players, six of whom were playing Monk/Somethings or Rogue/somethings. All of the multi-classers complaining about how I outmaneuvered and out-fought their characters. Naturally! Game ended because the GM decided that some of the players were obnoxious and a few were too sporatic in attendence.
I still talk about this character as having been a great concept that was fun to play.
2> Monk/Wizard with a 41 point build. GM wanted to get us up in levels fast, so he was advancing us about 1 level per session. Unfortunately, he first got demoralized when one good player left, then he brought in another player who immediately went on an "I refuse to play with so-and-so" binge until the GM finally called a halt to the game.
3> Current PC. A straight Wizard build, 4th level. Really enjoy playing him despite some of the handicaps Wizards present to my normal gaming style. But the GM has some issues with the way the game is going and with me specifically, so the game is now "on haitus".
Beyond those, I've seen more than one campaign end because the GM suddenly decided that he wanted to play a completely different setting or try something different. I wasn't as attached to those characters, but it still gets annoying to have a perfectly good game yanked out from under one's feet just because the GM decides he's bored with it.