Wanting to invest $500

Few things:

With Joeant, give me a good title, description, URL, and some benefits of your site, and I should be able to get it listed free.

With GoGuides, I have an editor username somewhere, but I cannot find it. Just volunteer to be an editor, submit a few sites, and then list your site for free.

I am one the few that still see the benefit of the Yahoo Directory. To see why, here is a thread you can view:
http://www.ozzu.com/yahoo-forum/yahoo-directory-worth-t53152.html

With the MSN Small Business Directory, I haven't seen it help in positioning for MSN, I believe it will one day, but it will help pass some decent Pagerank to your site. Make sure to do the optional business card, as I have seen a few of my client's business card showing up well in Google's results.

The most important, yet free, yet very hard to get into is DMOZ. You need to look for a category that fits your site, check out where your competitors are listed, check the last time that category was updated and submit your site. This will help you the most in Google's serps.

Then just get quality link exchanges.

If you are going to try some ppc with your remaining budget, you may want to try a smaller ppc engine like Findwhat, Goclick, Kanoodle or others. These will not bring in the visitors that Google, MSN, or Yahoo will, but the cost will be much less and you can test out different ad creative.

keep your money in your pocket.

start to submit your website to sime free directories and you will see the result in one month or two

i have done with my website and in one month has PR 3 and almost 30.000 uniques per month

and the site has only 3 months