One thing to keep in mind also is efficiency. I'm not much for saving the environment and all that stuff, but I do like to know my power supplies are being efficient! Not because I'm wasting less of earth's precious natural resources but b/c efficiency comes from a better overall design and quality of a product. There is a project group for power supplies called 80 Plus, basically it's a group starting a standard of power supplies having at least 80% efficiency all across the board. These power supplies don't cost much more than usual ones (a few dollars maybe) but they use a few types of technology to be efficient. Efficiency equals less heat and less of that power from your battery being wasted! I haven't really looked into it for small form factor or DC-DC power supplies, only regular ATX sized power supplies but check out their website.
http://www.80plus.org
Here is a list of recommended power supply units from their website as well
http://www.80plus.org/suppliers.html