If you don't need a built-in preamp, the old dbx166 is one of my favorite compressors. It's transparent and works on anything.
We're currently using Aphex Channels on all the mics in our facility. There isn't much control...so you get what you get for the most part, but luckily they sound perfect with RE20s. They keep everything dynamically tight and you can't hear them working, which I like.
For what it's worth, I used the Cloudlifter CL-1 or CL-4 on everything. It works magic on dynamic mic output levels without increasing the noise floor.