I recently read a brilliant book about the world of 'professional' scrabble players: Word Freak by Stefan Fatsis (Word Freak on Amazon UK, Word Freak on Amazon US). If you're at all interested in scrabble and even if you're not, I recommend it.
Having read Word Freak I realised how seriously some people take scrabble and that not any dictionary will do for legal words! Because the scrabble game is owned by different groups in the US and the UK there are two official lists of acceptable words and both are available online (sort of) at scrabble.com. The file available for download at the bottom of this page is (as far as I can tell) the "international" scrabble dictionary that contains all the words in both dictionaries
UK and Rest of World Word Checker
US Word Checker and Word Builder
Apparently my dictionary file was ever so slightly deficient as there are 96 legal scrabble two-letter words
Been mucking about with scrabble/countdown playing perl scripts and have compiled a list of acceptable two-letter words
aa, ad, ae, ah, ai, am, an, ar, as, at, aw, ay, ba, be, bi, bo, by, da, de, do, ef, eh, el, em, en, er, es, et, ex, fa, go, ha, he, hi, ho, id, if, in, is, it, jo, ka, la, li, lo, ma, me, mi, mu, my, na, no, nu, od, oe, of, oh, om, on, op, or, os, ow, ox, oy, pa, pe, pi, re, sh, si, so, ta, ti, to, un, up, us, ut, we, wo, xi, xu, ya, ye, ag, al, ax, hm, mm, mo, ne, uh, um
There's 94 (from a 26^2 or 676 possibilities)
If you want all the legitimate words in scrabble you can download the scrabble words file (296KB zip file) (I believe this file contains both US and UK words)
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