I got a Pisen battery from Dealextreme for $7.50 that seems to work pretty well: http://www.dealextreme.com/details.dx/sku.39142

They also have a $3.10 one that I recognize as similar to an awful generic BL-5C that I bought from them, that has about 1/3 the capacity of the original. The Pisen seems pretty comparable to the original Nokia cell in my E63 though.