At present, you may do what you want, but the trend is apparently toward website – one word, lowercased. When two words express a single concept, they tend to grow together, sometimes passing through a hyphenated phase. The transition from Web site (from "World Wide Web site") to website has been quite rapid. For a brief but thorough discussion of this topic, check the website entry in the online American Heritage Dictionary.  (Note:  When we began this site, we tended to use Web site.  More recently, we have seen evidence that Website or website is widely used.  Readers may therefore observe some inconsistencies in this Web site . . . er, Website . . . er, website.  We've given up trying to be consistent when usage is in transition, but we at least try to be consistent within any given entry.  To paraphrase Emerson, this is one hobgoblin that we'll not allow to bother us.)