Aside from that, there are three ways to make money on twitter not related to having your own website up
1) CPA offers that pay you for clicks to their website
2) Dropping Affiliate marketing links (duh)
3) Letting people pay you to publish their tweets
I have experience with 1 & 2. Only heard about 3 so it may be BS. However, since my twitter accounts were established to drive traffic to my own sites, I generally only drop one or two links a week for CPA and Affiliate offers. Its just a way for a small amount of supplemental income. If it's the only thing you use your account for, you could push the envelope more. Just make sure for every tweet advertising one of your links, make two tweets about unrelated things. I use famous quotes, jokes, rss feeds from some good websites, etc. If all you do is drop affiliate links, you wont keep any followers worth a damn.