Congratulations on the head. I kind of want one of those, even though I really can't justify it, but I'd love to have a beastly true stereo setup for effects laden 6 string stuff. But I have essentially half of one of those (the AH 600-12), which is awesome and is currently my main rehearsal head, and sometimes gigs
Anyway, I think a good choice would be a couple of the GK NEO 212s. 600w a piece and sound great and about 50 pounds each. If you're going to cart around a nearly 50 pound, 1200w head your cabs should measure up. Like a pair of single 12s is going to just be ridiculous with that head. I would you definitely want a pair of something to take advantage of the dual power sections (whether or not you ever use the stereo capabilities), and I would say 2x10s would be the smallest you'd want to go. So 2x10s, 2x12s, 4x10s, or maybe 1x15s would be the way to go. I use my 600 with a Genz Benz 410, an SWR Goliath III 4x10, or a pair of Genz Uber Quads (each one has a 12, 2 8s, and a tweeter, and I would consider equivalent to about 75% of a typical 4x10 in terms of volume).
But you can't just go with a cheap 200w 2x10. The smaller you try to go, the more high end you'll have to go to have the power handling you need. And at some point numbers just become numbers and not a representation of real world actualities. Like if someone tells you they have a 1000w 2x10 cab, they're full of it. So be wary of speaker cabs that are way on the small side yet boast seemingly impossible power ratings, because they probably are impossible.
Anyway, good luck.