What Elder_Basilisk said.
In addition, there is a point to be made that taking levels of fighter past Ftr10, or even past Ftr4, is completely pointless. If you are a human, dwarf, half-elf, half-orc, or halfling, you're better off ditching fighter, because fighter abilities don't scale with level. (Annoying, but true; feats, the fighter's bread and butter, are BAB- and feat-dependent rather than level-dependent.)
Thus, Ftr4/Bbn16 (or Ftr4/Bbn1/PrC10/PrC5) is a great multiclass, and will be even better in 3.5e, when the barbarian gets greater rage and DR sooner. Ftr4/Sor1/other fighter classes is nice for
shield,
true strike, and
expeditious retreat. Ftr2/Pal1/Templar2/Clr15 is REALLY nice; you get the magical +16 BAB (allowing four iterative attacks), GREAT saves (between the pally's divine grace and cleric's saves), and 8th-level divine spells.
Spellcasters should go single-classed, or take a +1 level PrC, unless you take only one or two levels (like the Ftr/Sor above), or take one or two levels of a non-spellcaster class to add a nifty ability. Monk 1/Druid 19 is a great multiclass (Wis bonus to AC and evasion are very nice), as is Pal1/Sor19 (your spellcasting stat adds to your SAVES!).