I have a pair of Nisi sprint rims 28h. They're silver, and the type with eyelets (not the ones where you need washers). I built them up as fixed gear wheels when I used to be tester and wanted to copy Boardman and Obree. After a couple of training rides, I decided it really wasn't for me, so they have hardly been ridden at all. They're not the stupidly light pista ones; I think they weigh in around 400g IIRC, so same ball park as GP4. Since I didn't ride them for long enough, I can't comment on their robustness compared to GP4s, but I've read good things about them.
Let me know if you're interested at £20 + post (or could deliver if not urgent...)
Nick