<p>What tool or method do you recommend to find and replace values in your code? If code is on Linux/Unix, are find and grep the best method?</p>

I'm assuming you intend to rename a variable.
It depends on what the body of code is. For C#, Visual Studio's renaming tool is very good. Remember that for it to work reliably, you need the renaming to work hand in hand with the compiler/interpreter, so you can make sure you only make the change in the right scope.
If it is a very simple find/replace, surely the lowly notepad would do an OK job?