Note: We strongly dislike advertising networks such as Magpie. That being said, here is a list for reference purposes.

• adCause.com: Twitter Ads -Advertise on twitter. Keep the money or donate all or a percentage of your earnings to your favorite charity or cause. Buy and Sell ads on twitter! (follow us @adcause on twitter)
• FeaturedUsers.com - If you’re a Twitter user, it’s a great way to get more followers and support your favorite 3rd party Twitter apps. If you’re a Twitter app developer, it’s a simple way to start monetizing your application.
• Magpie - Convert your tweets into bling-bling by allowing Magpie to post tweets in your timeline or build conversation around your brand by having carefully selected key-influencers spread the word just for you. (click to watch funny video!)
• Twitchance.com - Twitchance is a free Twitter lottery. People post a sponsor’s message on Twitter to become eligable for a cash price (viral marketing).