Anyway, this time all I sent was some art work (in the pop art and comic book styles). I wrote a really short letter (the shortest I've ever written to a celebrity). I basically said I thought he was an awesome actor, that I was sending some art work I made (I'm a Graphic Design major at university) and that I'd love to hear his thoughts or suggestions on them (although if he wanted to send an autograph that would be cool too.) ;D
I received this on August 16. The signature on the right is pre-printed on the photo and the signature on the left is what he wrote himself. Notice that he crossed out "Ricky" at the bottom and added "Raviv". I'd say it's safe to say that he's going by his real name now, on and off screen.

Needless to say, I'm pretty thrilled with this success!
The address I used was
No envelope.Raviv Ullman
c/o Nani/Saperstein Management
16 Penn Plaza
Ste. 722
New York, NY 10001
USA