Here are some thoughts on fixed/ss bikes that I own/owned/have ridden. T
KHS Flight 100:
Very light and stiff frame. More of a racing geometry than some other options, but I really liked this bike until I bent the frame in an accident. The toeverlap is pretty significant and the handling is responsive, bordering on twitchy, like you would expect from a track racing bike. You need to be extra vigilant riding this around the burgh because even relatively small bumps and potholes can be jaring.
IRO Mark V Pro:
Definitely heavier than the flight 100. Less toeverlap and a more relaxed geometry. This is what I'm riding right now and I'm pretty happy with it, but I really bought it because I got a great deal on a lightly used frame on ebay. The flight 100 is more fun imo if you want something sporty, but this is a nice reliable commuter and absorbs the shocks of less than perfect roads more favorably.
Surly Steamroller:
Very similar to the IRO Mark V, IMO. About the same weight and similar frame geometry. I've never owned one, but know a couple people who do and have ridden the bike a few times. Solid all-around choice for commuting.
Bianchi Pista
The classic. Sightly more expensive. Not quite as tight geometry as the flight 100 and likewise slightly less toeverlap. Much more of a track racing bike than the Mark V or Steamroller though. Thicker gauge steel than the flight 100 and its a touch heavier, but lighter than the Mark V or Steamroller. Thank god they stopped making the chome version of this frame; hideously flashy. You look like your riding around on a frame made out of hotel railings.
Origin 8 Uno
Another decent commuter along the lines of the Mark V or the steamroller. Even more relaxed geometry and even less toeverlap. Cheaper, but it not clear to me that this is really because its a lower quality bike as much as its just a less well known brand. I haven't ridden one long enough to say for sure.