I don't know living greyhawk, but if psionics is allowed, aim to get into Pyrokineticist prestige class ASAP.
Otherwise Sorcerer is my favourite. Strangely many fire spells don't set people alight (I think burning hands may still do so). Useful feats that are probably unavailable to you include clinging spell (a spell variant of clinging breath from draconomicon) and the searing spell (name?) from Sandstorm which allows fire spells to affect creatures with fire resistance or immunity.
n.b. burning hands text, my emphasis. Still your best bet for setting light to people.
A cone of searing flame shoots from your fingertips. Any creature in the area of the flames takes 1d4 points of fire damage per caster level (maximum 5d4). Flammable materials burn if the flames touch them. A character can extinguish burning items as a full-round action.
Flaming sphere is a useful 2nd level spell that can set light to flammable things it touches.
A Wall of Fire can probably set people alight since it isn't an instantaneous burst like a fireball, but it isn't stated in the spell description so the DM may not allow it.
Of course, another interesting alternative might be a firebombing rogue - lob alchemists fire and get flaming sneak attack damage (I think that is allowed, better check!) and it will set people alight. Get a Hewards Handy Haversack or similar cheap CRPG-style item as soon as possible to carry them safely!
Druid is another possibility, with produce flame, flaming sword, flaming sphere, flame strike and summon natures ally - from 3rd level onwards you can be summoning small fire elementals to ignite people, and ultimately you can turn into a fire elemental yourself. Cool eh?
Cheers