I recommend a BOSS OD-3. It's very smooth, and it'll sound good with your amp. If it's out of your price range, just save longer: it's worth it.
Something like the DS-1 won't be as smooth as you want. And the SD-1 is basically a Tubescreamer clone, and you don't want anything that claims to be a Tubescreamer since you have a solid state amp. It'll just make it sound like poo.
Stuff I use:
Standard Strat with Lace Hot Golds; Standard Ash Tele; Fulltone OCD, Line6 M9