I used J-B Weld. I love the stuff. It stiffens slow so you can work with it, and dries overnight so you can sand it.
The only mistake I made was not doing ALL the cracks, I only did the big cracks and chips. After I painted the wheel with Black Rust-O'lium Applicance Epoxy, I could see even the smallest cracks. Take your time and get ALL the defects out before you paint. Since you see/hold the wheel all the time, you'll be glad you spent the extra effort.
