For me, I'd have to say...
1. Telflammar Shadowlord (WoTC - Forgotten Realms - Unapprochable East)
Pretty flavourful and I find the abilities are pretty original and interesting. The spell column is nice, and a part of me just loves the fact that you can 'buy' your way into this class.
2. Candle Caster (WoTC - Tome and Blood)
Simply for being completely different. A class built around crafting and using magical candles. Very nice.
3. Risen Martyr (WoTC - Book of Exalted Deeds)
A good way to keep a PC or NPC around until the competion of a quest of divine nature. I don't know, weird classes like this really interest me *shrug*.
4. Fochulcan Lyrist (WoTC - Complete Adventurer)
It's nice to see a class that reminds you of something from an old edition, and I like how this one lets you be creative on alternate methods to complete the entry requirements.
5. Master Thrower (WoTC - Complete Warrior)
A halfling rogue throwing skiprocks and tripping twelve enemies a round made me fall in love with this class. I like classes that give you a theme and different ways to customize it (Exotic Weapon Master being a similar class, though not as good as this one).
What about you?