OEM axles aren't going to be any stronger, whether they're ITR, GSR, Si, etc. Some good aftermarket axle manufacturers are Gator and DriveShaftShop...I've got Gators in my CRX right now, and I love them. Before that the axles were in a friend of mine's 11.30 hatch, and before that they were in my old allmotor 89 hatch...so they've taken over 2 years of 200+whp abuse, and still have zero problems. DriveShaftShop, on the other hand, I'm not too fond of. Another personal friend of mine had the DSS stage 3's with upgraded DSS hubs, and broke the axle shaft REPEATEDLY...I've noticed on H-T that many people feel exactly the opposite (Gator sucks and DSS is the shit), so I'm going to venture out and say that they're both good axles, and like any other product some people have bad experiences and some have good experiences. I can personally vouch for Gator axles being the shit, though.
Another factor that will affect your axle breakage is how low your car is (the lower your car is the more your CV joints are put in a bind, and will cause them to wear out and/or break) and what type of clutch you have. A puck clutch (or a stage 3/4/whatever) is going to beat the hell out of your axles on hard launches, whether you've got high HP axles or not.