I recently wrote about Ross Carter's Snow Leopard Creater Code discoveries and his solution, LaunchCodes. It turns out there were a few issues with the initial implementation, such as Apple Events not being passed along. Normally when you find a file in Spotlight, a PDF for example, opening it launches Preview and the query that was used to locate the file shows up in the search field in Preview. This was no longer working in LaunchCodes, though Ross says he's working on that right now. In the meantime, Michel Fortin has produced Magic Launch, and it solves the majority of the issues that have been presented.
Magic Launch installs as a System Preferences pane, and you can drag and drop applications to it to register their file type. Then, you can choose a default application, but optionally specify that it should launch in it the application which created it, when possible. Probably the coolest feature, though, is the rule handling. Similar to rules in Mail.app, you can set up a series of criteria to determine when a different app should open the file. You can have multiple rules, and each rule can check things like file location, file name or extension, text contents, hex contents and/or ASCII contents. That's pretty nifty, and goes beyond the default functionality that was available before we even needed apps like this.
Magic Launch is free to try out, and costs $14US for a license. If you're still finding documents annoyingly launching the wrong applications, go download it and give it a try.