Stalker
Fighter-Thief
Thief
Paladin (either wizard slayer or undead hunter is excellent)
Fighter-Mage
Mage

If you can hold out that long, playing a couple human fighters and dual classing them to thief/mage at 9th or 10th level is definitely worth it, but that prevents using them as thieves or mages until BGII unless you mod the game to remove the XP cap (and even if you do, it will take a LONG time to get them to 9th or 10th level in BGI; wasting ankhegs just does not provide enough XP.) Your best bet is probably to just multi-class a couple elves and thank Bioware the AD&D 2nd ed. level limits for demihumans do not apply in BG. A F/M/T is a total badass once he starts getting 9th level wizard spells, but even if you avoid beating ToB that long, your party will be so overpowered the nigh omnipotent F/M/T will be hard to appreciate.

Anyway, the above party easily provides enough hitting power for stand up fights, enough spell casting for heavy artillery, and enough stealth to not only scout but do recon in force. You probably noticed I did not include a cleric; that is because the paladin and relatively plentiful healing/antidote potions should cover all healing needs, or a trip to the nearest temple after a really bad fight (just remember: Elves cannot be resurrected.) Worst case scenario, you are wise to save before all big fights anyway, so you can always restore if stomped too badly.

If you REALLY want the cleric, you can probably replace the straight class thief with one. However, I like the ability to send the top half of my party in hidden, then half each of them backstab a different spell caster as my artillery and dragoon come into sight. Usually half the enemy party goes down at the start, then I double team the rest, and things end pretty quickly. Also, as noted in my response to Legolas, with only one thief you cannot have a character who is really good with ALL thief skills; with two you can have one specialize in picking pockets and the other in picking locks, while maxxing out the hide in shadows, move silently and detect traps on both.