From Internet.com 67 Open Source Replacements for Really Expensive Applications.
I have had recent experience selecting and recommending software in a number of these categories and this review echos my own results in many areas.
Essentially, even if you need commercial support, many open source programs now offer paid support that costs much less than the alternatives.
The lists at Datamation tend to stay up-to-date and are always worth the look. Check it out and see where you can use a quality open source package if you choose not to purchase software.