Christian just pinged me this URL keywordfinder.org. It’s a tool that will retrieve the 20 top search terms related to the term you enter. This tool is based on the recently launched enhancements to Yahoo! BOSS. Uwe has done something similar as part of his premium tool LinkCheck (German site).
Here is a sample SERP
Nice and handy tool to get a quick idea of what terms are popular in Yahoo!’s web search.