The only DW games out are for GBC- if you want, you can get DW3 which was great. For GBA games though, Tactics Ogre and Aria of Sorrow definitely. If you know anyone else with Tactics Ogre, you can play the duel mode which is pretty cool.
<img src=“http://www.rpgclassics.com/staff/tenchimaru/td.gif”> The Duel Mode also nets you a few unique emblems, so try and find someone.
Aria R0x0rz. 
imo, aria of sorrow is the best gb castlevania. i found it a bit too short, though…i got it about 2 weeks ago and i’ve already gotten all the endings.