that I built a few years back is still working for me -- actually, built two versions as I updated to the v2 version and then added the resistors around the data pins to keep some devices happy to move to v3. Check MintyBoost in a Google search for more information on this DIY project. I think the kits have been out of stock for the last while but the instructions are still there including the last mods to the kit (
http://www.ladyada.net/make/mintyboost/parts.html ). The parts list has the updated schematics for some odd reason.
The last one I build used three D cells in series (staying below the 5V maximum) and worked quite well on a long camping trip for keeping the our devices charged other than the daughter's tablet which needed about 1.4A through a micro-USB connector to charge.
While a fairly simple project, it's more for those who enjoying tinkering with electronics or want to start doing so.
Regards,
David