I started riding fixed at 48 x 16. After a couple of months I dropped to 48 X 17, which I loved and rode for more than a year. Most recently, for kicks, I just got a Sugino Zen Messenger 45 tooth ring for the front and have ridden it with 15, 16, and 17. For the past week or so I've been on 45 x 17 and I really dig it. It's easier to slow down and skid (skipping doesn't feel any "easier" though).

This is the lowest gear I've ever gone with (which really isn't that low, it's still low 70s, about 71 or so I think). I remember Greg Goode writing that he rocks gearing in the high 60s, which is what he recommends.

Obviously a personal preference. IMO that cogs aren't that expensive. Get a few, see what works, and sell or trade the ones that didn't suit you and take a slight financial hit for the learning experience. I would say to play around with chainrings too, but they are quite a bit more pricey.