A F/T is a better tank than a regular fighter, b/c he gets to use UAI and load up on stuff with physical damage resistance like Jan's armor and so on.
Wizard Slayer can theoretically be cool if you alternate between regular darts (speed factor 2, so fast as lightning) and Crimson Dart +3 (speed factor 0, booyah!) With 3 base attacks per round you can get 4 ApR right from the beginning of the game (or 5 with GM patch/fix/hack). Use Crimson Dart against your typical spellcaster, and use the regular darts against mages with PfMW to paralyze them. Against regular enemies you can try Dwarven Thrower +3 or Boomerang Dagger / Firetooth.
Against people with Improved Mantle or PfMW + are immune to normal weapons, you can use Fire Seeds + GWW [img]smile.gif[/img] I think Improved Irenicus would go down really easily with that combo. No matter what defenses he uses - PfMW, Improved Mantle, invisibility + SI
iv + SI:Abj + Prot. from Fire - you can hit him and inflict spellcasting failure. In late game K'logarath + GWW does a ton of damage.