best multi or dualclass combinations

[Justarius]

Here are some lethal/amusing combo's I've found good.

The Magekiller

Start with a mage (I chose abjurer) and dual class to fighter at third level. The reason for this is to be able to use mage items even though you'll essentially be a fighter and wear tank armour for the rest of your adventuring days. Having identify and mirror image is a nice bonus.

Throw your points into two hander style and the quarterstaff with any leftovers going to two handed swords. Now go and get that Staff of the Magi and become magic users worst nightmare.

Every hit from the staff will dispel magic on the target, generally removing all those pesky spell protections mages have. As a fighter you'll hit hard & hit often with the staff. A hit doesn't need to do damage for the spell to go off so stoneskin etc doesn't help. Having access to protection from evil, invis at will, spellshield and -2 AC as a fighter is all good.

Swashbuckler to fighter or cleric

The swashbucklers AC bonus stacks with tank armour. If you dual at 10th you'll get +2 to hit & dmg & -3 to AC. As a thief who's not going to be using stealth (because of the armour) you can concentrate on skills like find/remove traps and pickpockets. I've done this with both a fighter (styled as a blademaster) and cleric (priest of tymora) but expect it to work well as a mage base as well.

[Hazim ibn Gorion]

The PnP kensai's thac0 bonuses are "counts as" bonuses. So he can hit monsters that require magical weapons to hit, even when using a non-magical weapon. Don't have the PHB handy, but I'm almost positive that's the way it works. Played a PnP kensai once several years ago, and this is how my (pretty experienced) DM ran it. Like I said, it works just like the monk's fists.