Consolidating your servers is all the rage, especially since you can save money by doing it. You can save not only on the hardware, but the licenses.
To do that properly, you need a strategy. You start by detailing what you have, and then lay out the apps and where they could go.
Microsoft has a tool that can help. It's free, and easy to use. It will help you find not only your SQL Server servers and detail those, but also Office, Windows, etc. And it has LOTS of guidance on what to do next. Check it out here: http://technet.microsoft.com/en-us/library/bb977556.aspx