On special occasions Topaz Labs does provide big discounts on their bundles. Their website also provides tutorials and tips for using their features.
For an artistic effect I like this curly idea using the feature Topaz Clean.
This was a photo I took years ago with a 3.1MP camerae. It didn't come out all that well but I used Topaz Simplify Oil Painting to produce this effect. It went from being an over exposed drab photo to something artistic and interesting.
Copyright Nadine Spires 2012
Topaz Labs, as mentioned in a previous posting, is also used in HDR photos. http://www.topazlabs.com/blog/pro-insights-with-blake-rudis/
There are trial versions available and are worthwhile taking a look at. http://www.topazlabs.com/