As a DM, I rarely run a campaign with more than two chars. I find that there are essentially three combos which work best:
1) paladin and ranger
2) cleric and wizard
3) two bards
The paladin and ranger compliment eachother with their ability to stand and fight but also their ability to get out of the action should the need arise. Ranger (of course) acts as striker and Paladin as leader/defender
The cleric and wizard are less effective at survival but can deal tons more damage than the other group, its probably a good idea to get the cleric's armor prof. up as high as possible.
The two bards: BEST DUO EVER! Both can cover the basic essentials (hide armor + high dex = invincibility) and both can deal with almost any situation, healing eachother, providing rogue essentials, and can multiclass apart from eachother depending on the circumstances of the campaign.
The man in black fled across the desert, and the gunslinger followed...