Cruisemount and Customized Cycles are the only two (that I know of) out there. The differences betwixt them is placement of the module. Price is virtually the same when all's said and done. C-mount gives a 5% military discount though.
With C-mount you have to buy the correct module from Harley (I got mine from ebay for half the cost though so price can vary if you're patient/lucky) and then buy the rest from them. They supply detailed instructions, cables, mounting hardware, etc. It mounts, usually, on the left side, in front and above the passenger's foot rest. Thier web site has all the info and pics.
C-Cycles sell you the whole shebang. The placement is practically the only "nook" on the bike. You have to remove the back tire and fender. Their website has pictures.
I chose C-mount because I didn't have to remove the tire and fender; the rest of the installation is practically identical. This has been the single best investment I have made for my bike!