Highlighted words are common; grey words are rarer but in the dictionary. Lists use an open-source English word list, not the official Scrabble lists, so a few entries may not be valid in a given game.
The complete two-letter list
A B D E F G H I J K L M N O P Q R S T U W X Y Z
A
16B
5D
3E
10F
2G
1H
5I
5J
1K
2L
3M
7N
4O
14P
4Q
1R
1S
3T
3U
6W
2X
2Y
3Z
1Why two-letter words matter
Two-letter words let you play parallel to an existing word and score on two lines at once. The ones people forget most: qi, za, xi, xu, jo, ka, ki, oe, ae, ut.
Words that start with a vowel (51 of them) are the ones you reach for when the board is crowded: aa, ab, ad, ae, ag, ah, ai, al, am, an, ar, as, at, aw, ax, ay, ed, ef, eh, el, em, en, er, es, et, ex, id, if, in, is, it, od, oe, of, oh, oi, ok, om, on, op, or, os, ow, ox, oy, uh, um, un, up, us, ut.
Vowel dumps and the Q
Holding too many vowels? AA, AE, AI, OE, OI and OY burn two at once. Stuck with a Q and no U? QI is the only two-letter answer; see the Q without U list for longer ones.