If you are using Twitter, then you should also be using Tweetlater, which allows you to automate many of the processes which you need to do to make the most of Twitter eg send a welcome message, auto-tweet, auto-follow, auto-unfollow and so on.
Even if you are not using Twitter and tweetlater, a quick look around the tweetlater site reveals an interesting idea for banner ads and raising revenue from your website.
At the top of every page, above the fold, is a featured user banner. This reaches a large audience, both through the website and inclusion in 30k emails that are sent out. In order to feature here for 24 hours, all you need do is bid in the auction.
This is an interesting idea to deal with unsold inventory, raise money, and also promote your website as anyone who wins an auction will also mention your site in blogs, tweets etc. Particularly if they see an increase in followers from being featured.
Setting up persistent auctions such as this is not difficult, and could prove to be a valuable revenue generator for any site with a reasonable number of page views.
From an SEO / Web PR angle, purchasing a banner in such a way and on such a site will gain you a useful backlink, even if only temporary, whilst also getting your name and details out through email marketing to a large number of potential followers, customers etc. And very affordable, looking at the prices of previous successful auctions.