Adom - super weird initial keymap(you can change it),escape opens spellbook and other oddities.
T.o.M.E - I guess you know that one,overwhelming from the start,a little too much for my taste.
UNnethack - 3.6.1 comes with a nice tileset,standard nethack tileset + specific complements;higher versions
tileset (dawn something) is a convulated brown mass,what a waste of time and effort.
All in all I find DCSS superior,once you know that game it is impossible to fall back to any other roguelike's
interface.
Other:
Not a roguelike but it is special in the eyes of many - Heroes of might and magic *3*,very easy to get into,
then an incredible depth unfolds with player made maps and expansions.Really worth the 10$ if you can find it
on ebay or such .
Diablo2 as mentioned above is in a very bad shape atm,servers constantly crashing for months now due to some
bug users.
Ultima online can be played as a dungeon crawler,its free,just get on a public freeshard,ignore other players.

Also have a look at the dwarf fortress home page forums,in the other games section are tons of interesting games
talked about,I use that as source of general game info.