I like Bix Heavy Duty paint stripper. Its heavy duty, and you can buy it at your local Home Despot.

But honestly, unless your old paint is actually peeling off, don't strip it off, just sand it lightly to give it a rough surface, and prime and paint over it. It will work great!

You can use body filler to fill the dents if you want, but I usually ignore them. Unless the dents are really big, or your frame is a really light steel (like Columbus SL or SLX), then don't worry about frame integrity.

peace,
sam