Has the A138 been working for you? I ended up getting a few A46 tips instead of the micro USB tips because my local Radioshack had them on clearance for about $2.50 a piece. The micro USB tips were $10.
The A46 is a female USB-A connector so it will work for pretty much anything that uses USB, provided you have the proper USB cable to connect it. I got a few 1.5' micro USB cables from monoprice for that part of it.
I haven't used these enough to notice if it's charging significantly faster/slower than the stock charger, but it seems to work fine. I wish iGo would publish the specs for all the tips (amps, volts, etc) instead of just listing compatible devices.