Remember that you have to rebuild the hub with the same lacing pattern as you had it on your other wheel. So if your carbon wheels had a radial lace, you have to lace up the new rim radially. If you try to change the lacing pattern the flange on the hub will be stressed in another way which can cause failure.
Sorry for the late reply. Cracked it in a race. DCCX, going up a steep rise with some tree roots that were exposed. I was feeling pretty good (late, but good nonetheless) and was passing a few people. Went up that rise pretty fast, must have hit a tree root, and that was it.
Took a big gash out of the tire and wrecked the rim.
I've cracked two Cane Creek carbon rims - one Aros 58 and one Crono 58 from back in the day. One consideration would be to contact Cane Creek and let them know you're interested in a new rim. They lace their wheels on site at their factory in North Carolina; hence, if they've got an alloy tubular rim laying around, they may be able to re-lace the wheel using the identical pattern. I've worked with them with wheel issues for years and have nothing but good things to say about their customer service.
Another reason to consider this option - Cane Creek had an awful time with sticky freehub bodies with their rear hubs back when they were making geared hubs. If the wheel that has the cracked rim is a rear, they may be able to give it a once-over and ensure that the hub is in good working condition before this season begins.
As Echappe, Katsu, and Britton have already indicated, any of their recommendations will be great, too.
Cheap and hard to break: Escapes! I've got three sets and love 'em. Slightly heavier than the Mavic's but the little aero shape helps shed grass, mud and sand - plus makes 'em a bit stouter, I imagine. I'd like to hear more about the R-sys'. I can't believe you'd run those in cross. Scary monsters!