i used this one
http://www.rcdynamics.co.uk/
awsome small foot print and very easy to use
mates have used the novak one just as good as it does whats its meant to but larger footprint
there is also this one on ebay
http://cgi.ebay.co.uk/Voltage-Booste...item4cf556b508
but very flimsy mate had one to try but it flexed and broke at the first meeting
hope that helps
neil