The San Jose Scrabble Club No. 21 has two-letter and three-letter word lists online, as well as other lists and study guides.
I'm pleased to see the DOoM "crossword game" (Scrabble) MUDs are still up. Used to play MarlDOoM, like, eight years ago. Play Scrabble online, in true Multi-User Dimension form. To avoid copyright infringement, the DOoM servers play crossword games of non-descript rules. You get a board, and must assign special squares and letter values yourself. But you can always play on other peoples' boards, and the game is moderated by a reasonably complete Scrabble-style dictionary.
Is learning how to MUD too much effort to play Scrabble online? Try Hasbro Interactive's excellent Scrabble "2" for PC. (Let me know if you're interested in playing a weak player. :)
