My favorite White and clear water-slide decal paper came from World Paper EDIT UPDATE: I see that their website is no more but you can buy their product on EBAY - made in the USA
INKJET Waterslide Decal Transfer Paper 10 sheets mixed 5 CLEAR and 5 WHITE #1 4861583164314 | eBay
You can also buy just white or just clear packs
Instructional video are still all over YouTube.com Just search "Inkjet waterslide decal" there.