I allow the duskblade (PHBII), and some of the fighter / wizard prestige classes (no to abjurant whatever, no to suileeman empire or whatever one).
Generally, the "right" way to view the fighter / wizard thing is, you are a fighter with some extra tricks. If you want to rely primarily on your spells, you'll quickly end up having your "best action" each round to be to cast a spell. If you play THAT character, you should look into just being that guy and wearing a dress. A rainbow cloak has been prepared for you! However, if you instead actually create a character that is a fighter with some magical abilities, you'll have something that plays more like Link and less like Gandalf, which is probably what you want. Fighter 10 / Wizard 10 is a kind of lame place to end up, but Fighter 5 / Wizard 5 / Bladesinger 10 should not be- and of course, level 10 shouldn't be "man it would be cool if I could hit something" or anything.
Look up:
Spellsword (Complete Warrior)
Blade Singer (elf, discussed officially here
http://www.wizards.com/default.asp?x=dnd/prc/20070403)
Duskblade (PHBII)
Eldritch Knight (
http://www.d20srd.org/srd/prestigeClass ... Knight.htm)
If you like swiftblade, I'll check it out to see if it's something someone in Caligo could do.
Remember, you only get 3 classes total, and only 1 can be a prestige class. So if you are a spellsword, you won't be a duskblade. I may extend 10 level prestige classes, however, just as I would be expected to extent 20 level base classes if the players had more than 20 levels!
Also note, there is also bard.