Ahhh this is a fun topic. I still haven't really got anything definitive, though I've been thinking about it for a while. My first thought was Jack or Jacky, which I'm currently using as my screenname for lack of anything better, since it's a nickname I've been using for nearly four years. But, while I like the name and I'm quite attached to it, I'm not entirely sure about using it as my real name, it doesn't seem quite right somehow. Also, I already have a cousin named Jack.
My middle name actually Martin, which I love, and I've been thinking of using that as a first name, since it's a name I like, and was my grandad's name. If I don't use it as a first name, I'll almost definitely keep it as my middle.
Other options are Daniel, which I quite like, or Laurence, which is a male long form of my birth name. (Laurie.) It just seems a little... over the top. Or something.
Bottom line, I'm still undecided.

Hopefully I'll actually be out to my parents and friends soon, because I really want some input from my parents and I think it'd help me decide.