good place to host a rails app?

I am having a hard time sorting through the available RoR compatible
hosts. I am looking to get substruct http://code.google.com/p/substruct/
running. What we need to be able to do is quickly set up new stores,
that will each have their own domain, all using a single merchant
account.

I've heard good things about slicehost, though never used them.
-R