I found 2 parts for switching converters that might be of intrest to people.
This one is probably for the more Electrical Engineering savy:
This one looks more like an enthusiasts part:
http://www.dimensionengineering.com/DE-SW0XX.htm (note they have a lot of different switching regulators, but not all of them switch up so look before you leap)

Two really good places to look for lipoly batteries.
For more high powered or longer lasting batteries:
For a cheaper price:

and remember from the wiki: Unlike the regular gumstix daughtercards, the robostix can deal with voltages upto around 9v

So if you are using a robostix I would go with the 7.2 double cell lipoly's......

        -Jesse W.