At the Search Engine Watch Forums, a member who read a post by Aaron Wall is curious to know if there is a tool that checks if there are any websites outside his domain that might have a 301 redirect pointed to his website.
Nobody knows if there is a standalone tool, but Barry suggests that you log into the Webmaster Control Center and see if there are any backlinks that might be 301 redirects.
If pages are properly 301ed, then the search engines should pick them up as back links.
So logging into Google Webmaster Central and clicking on your links section should show you all your backlinks (not sorted by 301ed redirects, unfortunately). Same with Yahoo Site Explorer.
It would be nice if a tool existed that would make this more visible (tsk, tsk, Matt!).
In general, however, if you wanted to check 301 redirects on a known URL, you could search for any of the the available tools. It's important to 301 pages that may have been permanently redirected or to avoid duplicate content issues (so you'd redirect www to the non-www version of the site or vice versa).
Forum discussion continues at Search Engine Watch Forums.