Me too. The new cast looks pretty cool (Star Trek FTW!), but I sure miss the cast from the first films.
My favorite voices from the old cast were:
1. Lee Tockar (Teridax)
2. Christopher Gaze and Alessandro Juliani (Vakama)
3. Scott McNeil (Tahu and Onua)
4. Kathleen Barr (Roodaka)
5. French Tickner (Norik)
If I could choose one actor to return, it would be Lee, because it's likely that Teridax will return in the future, and he just wouldn't be the same without Lee's voice.