The most audacious DIY amp in my opinion is the DynaMight. There's nothing inexpensive or easy about it. I've been hacking at one, and should dedicate more time to it when I get a couple other projects knocked off in the coming weeks. Take a look at that if you really want to go to an extreme.
You might also be interested in the Dynamid, as mentioned earlier. And speaking of which, I just sent more money to Dan Gardner tonight. Sooner or later, I'll put together one of these, too.
Another one I'm working on is Millett's SRPP ECC99 amp for the AKG K-1000. Interesting design, and he does have a circuit variation for headphones other than the K-1000. It's worth looking at, though be warned about the transformers. They must be ordered from England. They're about $200 USD for the pair and have about a 3-4 lead. I ordered mine around 5/1, so I've got another week or two.
Those complaining about test equipment accumulation are correct... the lab is growing.