I use Tomicogs on my fixed gear mtb, 34:18 or 34:19 depending on the trail.

Shimano XT-M756 front hubs are awesome on fixed gear road bikes with track bike chainlines and 120mm spacing. It's a front hub but it uses a 10mm axle (instead of a 9mm axle that a normal Shimano road hub would use), so you just have to replace the axle with a solid threaded axle long enough to fit your frame (Wheels Mfg stainless axles are great and super affordable) and add two 5mm axle spacers and you've got a nice, bolt-on specific fixed-only rear wheel for your track bike. The only downside is cog sizing for bolt-on cogs, which is limited by the bolt circle diameter of a 6-bolt disc mount. I think 16t is the lowest you can go.