ECF member, ViZi, has compiled a
comprehensive guide to commercial (and purchasable hobbyist) PV
mods. It includes a
battery table, which tells you which battery is used in each
mod (and what the mod's net voltage is). As you will see, there are not that many 5V mods to choose from.
Subtract from that list the Detonator that recently blew up in the inventor's face (in his pants pocket actually) and has been withdrawn from market.
Add to that list the Magnum (which
simulates 5V) shown in the guide itself.