Kojak gives a nice list of some diy projects. There is a lot of support for each one online and that means they can be made by almost anyone. I've done the Billie and the Ella(anther made by the same folks)and, while they may not be the best they are really good values and nice kits to start out with.
Depends on what you are looking for. Here is a short list of diy tube projects that are not quite as popular but a few, like the Bugle, are almost legandary in the diy community. Others, like Nachbar's, are very inexpensive and amazingly good for the cost.
* Ralph Power Buliding your Own DIY Tube Amp: Ralph discusses how he put one of Gary Dahls VV30B amp together. A nice intro read on how to go about it: http://www.intergate.com/~Rpower/buildamp.htm
* Fred Nachbars Mini-Blok SET http://www.dogstar.dantimax.dk/tubestuf/miniblok.htm
Fred has lots of info and provides a nice explanation of the circuit. Read his article on the little PP amp at his site too.
* Jeremy Epsteinss Fee Lunch Direct Coupled 2A3. A nice SET circuit and an online reading list to help explain it. http://home.earthlink.net/~ellenoler/freelunch.html
* Derek Waltons JE Labs 300b project. A really excellent presentation of Joseph Esmillas (JELabs) SE 300b. http://indigo.ie/~walton/300b.html
Deluxe Edition: http://indigo.ie/~walton/300bmk2.html
*The Darling SET: http://www.diyparadise.com/Darling.html
, AND http://members.lycos.nl/Aren/id12.htm
* John Sherwoods 300b Breadboard : http://www.homestead.com/sparkgap/amp.html
. Nice looking breadboard! If you are starting out do not think you have to commit to a chassis right away! It just complicates things sometimes. Complete with nice pictures of the circuit layout.
* 8W SE EL34 by Claus Byrith. Very nice articles that include a lot of theory. Check out his PP at the same site too: http://www.lundahl.se/claus_b_se.html
* Gordon Rankins Bugle 45 (Wavelength Audio site) http://www.wavelengthaudio.com/bugle.pdf
* Wardsweb Direct Coupled 2A3: Based on the Loftin-White design by John Day (1929) http://www.wardsweb.org/audio/dc2a3.html
* Pete Millets 829B: http://www.pmillett.addr.com/829b_amplifier.htm
* Aristidis Coumpas parafeed 45 (ala Kurt Strain) This is at the Audio Club of Athens Site. While you are there check out the Audio Papers section for lots of good projects. http://aca.gr/paper31.htm
* Randy Carters Il Monstro, 845-845: http://www.cognitivEvent.com/av_monstro.html
* Thorston Loeschs Legacy 300b: Based on the Western Electric 91 (WE91): http://www.fortunecity.com/rivendell/xentar/1179/projects/legacy/Legacy.html
* 813 Push Pull, transformer coupled. Based on Lynn Olsons Aurora (this one isnt so simple): http://www.izzy-wizzy.com/audio/powamp813.html
If you are interseted in doing a kit I have an outline of online tube electronic info that you might find helpful. Drop me an email if you want a copy.