First of all this is not a affiliate sales link or anything like this but a personal opinion about the recent purchase I made, Copywriting Scorecard for Bloggers (by Problogger Darren & Divine Write).
Specially if you are struggling with writing effective blog posts. This will be a good guide. Best part is it is only $9.97 (only valid untill 31/08/2010). If you serious about blogging and need to improve your writing skills then this is a must purchased ebook.
Tomorrow they are going to triple the price ($29.97) and I purchased it without a second thought.
and you may find it useful.