I had, in many areas, 7 layers of paint that i needed to get through to get down to bare metal(most of them were poor quality anyway).
What I used to remove these was this
Dawn Power Dissolver.
You can get it at your local grocer or at Walmart for about $2-$3 a bottle. Each bottle can cover a fender roughly twice depending on how thick you spray it on.
WHAT TO DO:
1) mask off any rubber like window seals as this stuff will eat them up too.
2) spray a nice even and foamy coat over the entire area you want to strip.
3) cover the entire area in kitchen plastic wrap. ( I also used masking tape to seal out air which helps the process but not a lot.
4) let the stuff sit at lease overnight. I let it sit over 2 nights and it worked a little better but 3 nights was too much as the stuff dried out too much.
5) pull off the wrap (and tape)
6) your paint just falls off so just use a plastic scraper and push it all off. (I also used a pressure washer after i scraped to get even more off)
Each application made its way through 2-3 coats of paint or primer. It also softens up body filler so you can pick it out with a small chisel or scraper.
Additionally the stuff isnt all acidy and wont burn you at all. In fact it cleans your hands pretty good and smells nice.
Here are a few pics. (warning... BIG PIX)
The dawn doing its work
A chunk of paint that fell off when i pulled the saran wrap off.
Paint peeled (came across some crappy bondo work)