If you’re into Linux or open source software in general, or just can’t afford the expensive professional applications, you may want to have a look at Ubuntu Studio, an offspring of the increasingly popular Linux distro Ubuntu, targeted towards creative professionals and enthusiasts, be that designers, film producers or audio specialists. Ubuntu Studio comes with an array of applications striving to offer free alternatives to the expensive industry standards. While I can’t speak on the quality of said applications as I haven’t tried them, I think Ubuntu Studio is a good endeavor that’s worth looking into.
If you prefer to stick with your OS of choice, you might like to bookmark this list of free and open source software for Windows and Mac.
Last but not least, I’d like to point you to a great article by Shahid Shah on open source alternatives to Adobe’s Creative Suite. Shahid has taken the time to “trawl through the World Wide Web to find out how everyone can benefit from Open Source to build up their own studio and compete against Adobe Creative Suite”. Good links in there.