M.A. Cotter is a very good one. Also RWD, and Verion. Jensen are commonly used as built-in to many higher end preamps. Bent Audio sells the Stephens and Billington kits and assembled units. Ortofon, Denon, Shelter, all have outboard units. Lundahl is a common brand of raw transformer for DIY use.
What's a good step-up transformer?
Everyone says how moving coils are so much better than moving magnets, but what they don't metion is that the signal is so much smaller you need a step up transformer to run it with most phonostages. I'm wondering what a good one might be. Audio Note seems to have the market cornered but they are not cheap.