I use, and recommend, a Transcendent Sound Grounded Grid preamp. If you upgrade the tubes and output caps, they are a great sounding pre at a great price, and are an enjoyable build.
Thanks for the recommendation Dan! This looks like a really cool project. I'm going to research it a bit more thoroughly. As a guitarist, I can really appreciate and prefer tube amplification.
For the interim, I just scored a vintage Akai PS 200C solid state preamp. I'm going to give it a full refresh. It wasn't on my list, but I hear they sound great. And being a rare piece, it has collectable value as well.