www.adderrobot.com is what i use. Cheap, and you can use it with multiple accounts without buying a license for every one.
I use it to promote my music groups, albums, and live shows. Myspace bans you REAL quick now for "spamming", which they file mass friend adding under, i'm sure you notice the many messages in your inbox that have a huge X thru them. Theres currently no way to bypass the CAPTCHA right now though which is pretty annoying.