I've been trying to remember all the D&D games I've played, and I don't think I've ever single-classed. I think I tend towards party support roles because I want to be a jack-of-all-trades sort of character, and that tends to take away from being really amazing at any one thing.
Class combos I've really enjoyed:
Bard/Rogue- Support/Skill monkey
Barbarian/Fighter/Duskblade(PHII)/Scout(Complete Adventurer)/Ardent(Complete Psionic)- Movement/grapple specialist combatant
Ranger/Fighter/Duskblade(PHII)- Ranged combat specialist
I think Warlock(Complete Arcane) is the first class I've ever considered single-classing, but I haven't actually played a game since I discovered the class.
