I found this FREE eBay search tool that lets you set up items to search for on eBay and then it notifies you via email if anything gets listed that matches your criteria.
You can set up as many searches as you want and set the time from 15 minutes to 1 hour, 3 hours, 12 hours, 1 day or 1 week.
I have been using this tool to find things on eBay, especially specialized or collectible items.
eBay has a search tool, but it is limited and only notifies once every 24 hours. I have found a lot of Buy It Now items using this tool that I was able to purchase immediately before anyone else even knew it was listed.
Again, this is a totally FREE tool.