>For maximum efficiency at low voltages you should look at SMPS chips
>with synchronous rectification. These can be up to 95% efficient.

Agreed.

>Unfortunately some of the niceer ones won't go up to 10v input
>( e.g. TI TPS62050 series), however at this low output current
>you may have a reasonable selection of parts to choose from.

That would be my comment as well. As another source look at Linear 
Technology, they also have some nice devices, and another couple of features 
is that at the end of their datasheets they list some other devices that 
could be suitable (leads you on a data sheet chase a bit like some of 
Russells OT posts), and they have excellent sampling policy, just like 
Microchips, 3 off of each of 3 devices no questions asked. 

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