You can easily increase your site’s income by a few hundred dollars per month.
This is for those of you who already got nice traffic going through their site.
Free up some space on your side bar or post top and put up a sign (image) saying ‘Space for Rent’. Rent it out for sponsors for a limited period of time, usually per month. If you are using WordPress, then simply add the image as a widget to the side bar through the menu.
If you want to sell cross site top-post or bottom-post area, then use plugins such as:
On image click, lead the potential sponsor to a page where you explain image dimensions, site’s traffic, specific traffic profile, niche etc.
Source of inspiration: the amazing Stuart Walker at http://nichehacks.com/niche-upgrades/