You'll find that a week passes by pretty quickly in Oz! I was there nearly a month and didn't see half of what I would've liked to.
Anyway, looks like you got the surfing down. Nimbin's not far from Byron if you're into the whole hippie marijuana thing - definitely an interesting daytrip.
Otherwise, it really depends what you're into and what your travel budget is for the week. You can hop on a cheap JetStar or Virgin Blue flight to Cairns, for example, and dive the Great Barrier Reef. Or you can hop up a short-ish way up the east to the Gold Coast for the beaches and nightlife. Just after that is the Sunshine Coast, where there's some beautiful rainforest meeting up with the ocean. You can also go out to Magnetic Island or Stradbroke Island or Frazier Island for some outdoor adventures or sandboarding or whathaveyou. Tons to do! Too much, in fact!