My blog gets a fair amount of traffic, I suppose, a lot of good natural links (PR5), and I get about $200 per month from AdSense and the rest. I have $150 sitting in PayPal that I want to use, but on what? I've looked at various tools to help understand how to target my SEO, such as Optilink, but are they worth it? I'm not doing as well as I think I should be on the more key keyword/phrases that I would like to be targeting.
Regarding SEO you should read www.announceabirthday.com/seomadeeasy.pdf a free seo ebook that can give you some help . You should also work on traffic not only from seo'ing your site but from PPC you could use one such as Adsung for advertising your blog. Also you should purchase signatures/advertise on related websites/forums as well as places like yahoo answers and google groups. There are alot of things you can do to advertise your blog etc some have been outlined here: http://blog.topsocialsites.com/?p=4 ok that link is for websites but you could easily modify this to your needs as a blog
Buy a couple of reviews / text links on authority sites in your niche. Or if you're creative enough you can make a contest. However if you're asking this question you probably don't even need to spend these money
use as a prize for competition to the winner who helps generate most traffic to your site! haha easy to say but hard to do though. XD