I got a barcode scanner from ThinkGeek. That will handle the thousands of books that are new enough to have the ISBN as a barcode. As for the older (and pre-ISBN) books ... a lot of typing.
One of the reasons I got the scanner is because in addition to books, I have DVDs, comics, etc., that all need to be cataloged. Plus, for anything else I want to organize (spare computer hardware, non-printed stuff I collect, etc.), I can print out little barcode labels and set up a database to catalog them, too.