Multi-classing? I like it.
What I have done with over half of my 3e PCs is to take 1 level of something, then a main class. If you do it immediately, it makes sense, and you can work it into your background. The rogue who decided to join the monk order, the fighter who is trying to leave his barbaric heritage behind, the wizard whose father raised him as a fighter, etc.
In terms of favorite combinations - 1 level of fighter, barbarian or ranger is always nifty for extra fighting prowess. Ranger for the twf - barbarian for movement and rage, fighter for a feat!
If you have a decent wisdom, and are a wizard, sorcerer or bard, a level of monk can go a long way. A small boost to your AC, a few hit points, hand to hand combat for emergencies and Evasion! to help you survive those fireballs when you don't have magical defenses in place. The bonus to all saves is nifty as well!
Most combat classes could also benefit from a level of rogue - extra d6 damage on surprise or flanking, great skill points - for cross-class skills mostly - almost make up for missing out on one Bab progression. Ranger/rogue or monk/rogue make especially nice combos.
A level of cleric, with the right domains, can round out a character as well. The ability to heal yourself in emergencies is not to be overlooked! The travel, luck or war domains also add some great abilities.
One level of bard gives you the perform skill and bardic music. Plus some handy cantrips - detect magic, light, etc. You'd only be able to your your bardic song once - unless you picked up that feat from Song & Silence.... Can be handy, but tends to slow down most classes without adding great benefits.
Sorcerer gives you two spells - if well chosen can be powerful. But watchout for spell failure. A Monk/sorcerer - level 2. AC: 30. 20 Dex, 18 wis, +7 shield, +4 mage armor. The key is to take spell that are *not* level dependant - the reverse of building a straight sorcerer if you will. Exped. retreat is a good one - but you can also get this from the Travel domain....
And while all of this is powergaming and min-maxing - Just ask yourself WHY does the character have a level of this class? And an interesting character is born. Did they find religion? Loose religion? Are they trying to 'get out and go straight' (one level of rogue) - Did they get kicked out of the monastery for something bad? Etc.
And that was my mini-article on multi-classes.
