One of the things I've always wanted is some way to do a simple search and replace with strings and something that can do this with a bunch of files in the same directory.

Provided that the files are pure ASCII text, it's possible to do this from batch files with small command-line programs such as CHANGE.COM and FIX.EXE. But as was said, a simple search-and-replace-in-files can be done much easier with any of the advanced editors like Textpad and Ultraedit. Unless you need the search-and-replace feature to be automated, the GUI interface of those programs is much easier to use.