Which is better assuming you have a web site that generates traffic? To run google adsense on your web site or sell your own advertising space? what would be the pro's and con's of each?

Adsense is great for young sites. Sites just starting out. When you create a site and first launch it, you will not be getting people interested in advertising, therefore, you can fill the void with adsense. Once the site is established and you clearly see a market interested in ads on the site, you may want to consider a mixture of both so that you can determine which method earns you the best return on your traffic.

Where do you find advertisers willing to pay for advertising space on your site?

Google search `text link advertising` and you`ll find some of the top companies offering this service.

Do both. So you have diversity of income sources.

Your site needs to be big enough for that....

You could always have a 'advertise here' page on your website ?

It won't.