I no longer recommend Site5; see: The Sinking of Site5
At the beginning of 2011, I began hosting my websites on Site5. I have been singing their praises and recommending everyone I know to them. Today iThemes publicly announced their endorsement of Site5 hosting (and how terrible Hostgator is too). I’m really excited about the development because iThemes is a major WordPress plugins and themes vendor, so their endorsement confirms my feelings about Site5. Also, the CEOs of both companies have been communicating directly which will hopefully result in even better WordPress compatibility with Site5. Check out the announcement post, Site5 has a 6-month free trial (!) for the iThemes community.