Went from 46-17 to 42-17. I like that starts are easier on the knees now, but I lost about 5 mph top speed.

48-18 on my Fillmore (singlespeed).

48x19 on the Kilo, great for my area where there's a good amount of hills.

Steamroller
47x19 Fixed 67.2 gi
47x18 Free 70.9 gi

Monocog 29er
32x18 Free 51.6 gi
32x15 Fixed 61.9 gi

50/17 Vigorelli
48/17 Soma Rush (w/ brake)
34/13 Milwaukee Bruiser

lets see....

road
49/16 (Bareknuckle in summer, Fixed, front brake)
49/17 (Bareknuckle in winter, Fixed, front brake)
48/17 (Rob Roy on road in summer, Fixed, front and rear brakes)
48/18 (Rob Roy on road in summer, SS, front and rear brakes)
45/16 (Centurion conversion, Fixed, brakeless - bike is stashed at my parents house in IL, and ridden in pancake-flat rural areas)
45/17 (Centurion conversion, Fixed, brakeless - this ratio used on really windy days)
38/15 (Rob Roy winter with touring tires, Fixed, front and rear brakes)
38/16 (Rob Roy winter with studded tires, Fixed, front and rear brakes)

offroad
38/18 (Rob Roy cyclocross, SS, front and rear brakes)
34/14 (Redline Monocog 26er, SS, Front and rear brakes - riding to trail)
34/15 (Redline Monocog 26er , SS, front and rear brakes - trail-specific ratio)
34/16 (Redline Monocog 26er , fixed and SS, front and rear brakes - trail-specific ratio)
34/17 (Redline Monocog 26er, fixed and SS, front and rear brakes - trail-specific ratio)
34/18 (Redline Monocog 26er , SS, front and rear brakes - trail-specific ratio)
34/20 (Redline Monocog 26er , SS, front and rear brakes - trail-specific ratio)
34/22 (Redline Monocog 26er , SS, front and rear brakes - trail-specific ratio)

The more you ride, the more you realize there is no best ratio. These are my general guidlelines, but it really depends on the day, the weather, the bike, and the terrain, and a lot of other factors. Having multiple rear wheels per bike really expands your options on a day-to-day basis.

46/19 for the streets out here

45x17 or 45x16 depending on how I feel. My city is very flat.

52X18

Just built up my first fixed off of a 78 Schwinn, kept the crank and outermost chainring, but boy it's uphill learning trackstands and skidding.

Track Bike : 52-16 (Front Brake for Street Use/Taken off when Racing)
Fixed Conversion : 42-13 (Front Brake)

52X17 FG with brakes.

Thats the stock ratio on my windsor, and yea im runnin front brakes. trying to get a 17 o8 tooth cog for the other side of my hub though.

for me, 48x17 is the ideal street gearing

46x20 at the moment, little bit too low for me but my LBS was out of stock on 18 and 19t cogs so I spinfor now

39x14 on my schwinn conversion. love them tiny chainrings

43x16 (which is about 72 gear inches, I believe).

hmmmm...no one said 46x16? that's me.

45-16

lol i did in my first post!

although just bought a 18t cog....gonna see how i like the slightly lower gear. want to learn to skid lol

47/19 fixed on my steamroller. probably gonna change to 47/18.

i get the feeling i will be flamed for asking this question lol, probably because i simple search would get an answer, but what the hell:

fixed gear skid stoppers: what ratio do you prefer to skid a little easier?

rode my build as SS for a month or so to get the feeling of the bike, in the past 2 weeks been riding fixed. would like to learn this skid stop technique, could come in handy....but having trouble doing it w/ the 46/16.
i have a 44t chainring, and a 18t cog coming in the mail. thinking 46/18 will be easier to skid on than 46/16 wihtout sacrificing too much speed....i guess if its still hard to skid, just for learning purposes, go 44/18...

38x16 w/brake.

Well, since I'm not much of a skidder, I won't comment on gear ratio, but I will say that you want an odd number of teeth in the rear cog to get more skid patches for longer rear tire life. For example, a 48 x 19 (68 gi) will give you 19 skid patches but a 46 x 18 (69 gi) will get you only 9 skid patches.

46x15 currently.

could use some more juice

true....yes i saw the skid patch number thing on sheldon brown....well, after i bought the 18t cog lol
buuuut i guess 9 patches isn't so bad compared to some other combination. perhaps i will get a 17 too....