I've enjoyed using plain ole' drum loops CD's...
I buy cheepies, they work just great for songwriting, and you don't spend 90+ bucks for the polish.
Check out the site
www.betamonkeymusic.com (15 dollar loops CD's--approx. 1000 loops per CD)
the guy sells CD's for Acid (wav format),they drop right into stereo tracks in PT, and with a little touching up, I am able to focus on songwriting.
Hope this helps