Tricks for easily creating BibTeX files

I wrote my last book (my only book, that is) using LaTeX. I had a large bibliography with close to 400 entries. I stored all of the bibliographic items in a¬†BibTeX file (a text file ending in .bib). Each item looks something like this: @book {Richeson:2008, AUTHOR = {Richeson, David S.}, TITLE = {Euler’s gem:…