I have built the Bottlehead Foreplay 2 and Foreplay 3 extended as well as the Seduction C4s preamp.
My next build is the Transcendent Sound Grounded Grid which is also a complete kit in a more conventional form factor. Info can be found on the Transcendent Sound website.
Tubes4hifi also makes some excellent preamp kits, both with, and without phono stage.
Audio Note Kits, now known as ANK Kits has some more upscale offerings.
If part kits are an option, or you want sand, the Pass B1 is very nice.
And the Aikido part kits are just fantastic.
Good luck and good listening.