The only DL media that is consistent enough for most of us to recommend is Verbatim brand.
Falcon FTI double layer disks are getting good user reviews here at cdfreaks now as well, but are not as widely distributed. Here is a list of companies that sell them: http://www.falconrak.com/agents_and_distributors.html
Burning to DL media I always use ImgBurn, though all of my double layer disks so far have been video. I've backed up dvds and made BD-9 disks using ImgBurn.
ImgBurn is the best choice, in my opinion, for setting the layer break correctly.