I would go with Bob Latino's ST-70 kits from tubes4hifi.com
They are new Dynaco ST-70 kits with improved chassis, connectors, and the VTA driver board. They're switchable between pentode/triode operation, and he also makes more powerful versions (ST-120 and M-125 monoblocks). It's a good way to get into the kit/amp building world as he provides great instructions. I would personally go for the ST-70 and work it for use with EL34's instead of KT-88's. The EL34's will give you more of that "tubey" sound. If your speakers are incredibly power hungry make the M-125 monoblocks. They're actually easier to build but would cost more.
If you want to start off slightly cheaper and simpler, Bottlehead makes a little tube headphone amp for a bit over $200. If you have have really high efficiency speakers (98db+), you could build their actual power amps, but I haven't actually heard those.
I have two ST-70's myself. I'm currently using a fully modded Curcio ST-70. While I really like the sound, the only thing it really has in common with the original is the transformers and the chassis. It's also just about the most complicated mod that's out there. The VTA ST-70 from Bob Latino sounds really good, and I'm actually considering ordering one and building another myself. Bob is also quite helpful.