Some time ago, I installed Enso (http://www.humanized.com) and fell in love with the easy and fast way of working. Tools like this can really give your productivity a boost. There is one disadvantage for poor consultants like me: Enso is not free (little less than 20 dollars). Nevertheless, this company is one to keep an eye on (check their blog as well, when you're at it) as other great ideas are under way.
This morning, I noticed that a plugin for Launchy (open source) has been created that enables to you to open already open windows. Launchy is free and the plugin as well, so this means that there is a free alternative to Enso. Well, not completely but I'll leave it up to you to take a look at both products and find the differences.