This has been discussed numerous times in here.. Particularly often between Southernspeed and I...
Other than the pre-made vinylly ones from LMC, which I'm sure someone is going to post up, your options are limited..
If you want something that'll conform, it's gonna require heat... I looked into it at one point... Unless your some sort of chemist that knows the particulars on what kinda rubber to purchase, then found it in applicable sheets from somewhere, it's gonna be a difficult task..
I ended up using truck bed mat, cut to fit in the flats... The only thing that doesn't get covered is the tranny hump.. I'll be doing a custom flat sided/topped one when I do my floors, so at that point I may be able to cover it easier...
I went with a big universal one, at the bottom of the page, and cut to fit...
http://www.pickupspecialties.com/bedmats.htm
here's a pic of the back... Also, I'll be Herculining the floor with a bunch of heavy coats, before I lay that done... thicker the herculiner the better...