I should have clarified that most of the items I sell are new with a fairly consistent pricing history for the last 2 weeks, so completed items search usually works OK for me. Using the mpire researcher often helps too (but the results you get can sometimes be a bit misleading if you don't know what you're doing).
You can find the mpire researcher here:
www.mpire.com/researchSearch history is 30 days, however, they only show what they call "Top selling listings", which shows only listings that sold above the average selling price. So, be careful, because it can be misleading if you don't understand that it doesn't show a true representation of how an item sells on eBay. It can be quite helpful if used properly, though.
Otherwise, you can use a paid service like Vendio or Hammertap to do your research.