Overdrive is usually the service for that. Nook, Sony and most readers that use ePub as reading format can be used.
Kindle 3 should be able to join as well at the end of this year.
Besides that, think about the online bookstore for your device. If you live in USA and you are into library lending primary, I would recommend Nook Touch. You will be able to enjoy B&N books as well or even the free in-store reading capabilities.
Compare prices too, and PDF capabilities. Sony is better reading PDFs than Nook or even Kindle 3. I do like landscape too, it's a very useful feature for poetry and IT books.
And welcome to Mobileread!
