This used to happen to me all the time. I used to walk for exercise, but then, when I started jogging, I went to a specialized footwear store (that caters to runners), they did a foot analysis. My usual shoe size is 7 1/2-8, and after that analysis, I ended up with a 8 1/2 running shoe. I explained about my toes going to sleep, and they said that there wasn't enough room in the "box" part (the ball/toe part) of my shoes, so they were pinching off some nerves. Since I switched to bigger running shoes, I haven't had my toes fall asleep once (at least while exercising). If I'm sitting cross legged on the floor with my kids for awhile, that is another story all together! I would recommend finding a specialized running/exercising shoe store and have them evaluate your feet. Good luck!
-Shellie