Here are a few ideas I've had:
B - Banana Beer
C - Colour, anything with colour in the name bar 'Red'.
E - Extra, anything with Extra in the name.
F - Fruit Lambic
H - High Strength, 15% +
I - Ice-Lolly IPA, you have to make an Ice Lolly out of an IPA!
L - Lambic, non fruit.
M - Milimeter, smallest cubic capacity wins.
N - Norse, anything with a relation to Norse mythology
O - Oyster Stout
P - Porter
Q - Quote, something used in the P round bar your own entry!
R - Red ALe
T - Triple
U - Unusual container, not the usual can/bottle. Can relate to the way the vessel is capped, what the vessel looks like, etc. Not to mean unusual designs on the can.
Yuletide - Christmas Ale! (Good luck, hah)
Z - Zebra. Beer from Africa.