For the jl 1000/1 I was going with the zero gauges wire and for the 300/4 I was going with 4 gauge.
IMO, 10 gauge would be fine on the 1K and 14 or 16 gauge would work for the 300.
For the hardcore in you, you can step up to 8 on the 1K and 12 for the 300, but I really believe thats overkill.
I used speaker wire from my local Dow/Marvac electronics supply. (10 and 14 gauge respectively)
If you want to blow the coin, I would personally use Monster cable (http://www.monstercable.com/caraudio2/).