A recent interview with Wired has revealed that another Castlevania DS game is in the works:

WN: What’s coming up next for Castlevania, the games?

KI: First, we’re doing another Nintendo DS version. There hasn’t been an official announcement, but we’re doing it. First, we want people to enjoy the PSP version, and afterwards we’re announcing it. So, please wait a little bit.

I’ve always enjoyed the Castlevania games for the GBA and the DS.  I hope they add even more replay value and engaging storyline in the next iteration in the series.