In the world of scripting anything, Mac or otherwise, commands and functions and routines (oh my!) are typically captured within pairs of brackets, parenthesis, etc. AutoPairs automates this for you on a Mac.
I suppose it's not truly automated as it can't read your mind and just know that you're creating a function or some other such bracketed hunk of script. But AutoPairs will automatically enter a matching ending bracket to the start bracket you just typed and put your cursor between the two, anxiously awatiing the brilliant code that is poised to spill forth from your fingers. Or something like that.
AutoPairs is a Preference Pane and an easy install. Be sure to read the ReadMe file that comes with it. You can specify applications that it will perform it's magic in, or leave it open to the default "most applications". I installed and set it up for TextWrangler, quickly opened a blank document and viola, matching brackets.
Perhaps one caveat is as I type this article it's also magically giving me matching pairs here in Firefox as well without my specifying it. For the purpose of this writing it's fine, and almost amusing. But I wonder if there's a way to disable it in specific applications as I'm sure that may be desired. I mean coding IS what we live for, but there may be something like 10% keyboard activity that isn't. But I'm going to play with it and see how this thing will impact my day to day scripting life.
Visit the developer's site and download AutoPairs here