A few months ago I discovered tinyurl.com. It takes a long URL and generates a short one for you. So http://www.amazon.de/exec/obidos/ASIN/3423202947 becomes http://tinyurl.com/q4wz, which is a dynamically generated redirection to the original page.
What can you use that for? Anytime that space is precious. I use it for ebay links in news postings, for links in IRC topics, for email messages and SMS. I even use it in my mail signature to make references for literary quotes 🙂
"Multiple exclamation marks [...] are a sure sign of a diseased mind."
- Terry Pratchett, "Eric" (http://tinyurl.com/evan)