A few things to think about:
1. Do you want 1/8" or 3/32" (there will be a much larger choice of components with 3/32")
2. Will you be able to get the gear inches you want with 48T (maybe it will work out quite expensive if you have to immediately buy another chainring)
3. I think square taper is more aesthetically pleasing, especially for track, fixed and single-speed, but maybe that's just me.
A few other places you could look:
http://www.velosolo.co.uk/
http://www.hubjub.co.uk/
Thanks Tim,
Some nice stuff on the velosolo site and prices aren't bad either.
There was some talk on here a while back about whether you should use a lock ring or not. Those bolted on cogs would obviously do away with the need for a lock ring but are there any disadvantages to having the rear cog fixed like that. Safety ?
Also, is a quick release skewer strong enough to hold the wheel in place?