Monkey Patching in Rails 3

What is the preferred way to Monkey Patch in Rails 3?

I just want to add a method to the String class. I'm more looking at where to place the file.

The initializer directory is a good place to collect all those little scraps. Since I tend to go a bit overboard with core extensions, I like to make a folder there called "extensions" and toss them all in there.

So, try /config/initializers/string_extension.rb, or /config/initializers/extensions/string.rb, or something similar. Either way, you can just forget about them afterward - Rails will require them for you, so you don't need to do it yourself.