I don't often advertise for people on this site, but I figured that this one's good for everybody. MacSanta is coordinating the use of a coupon code of MACSANTA to reduce the price of popular (and useful) Mac software by 20% through Christmas day. Read the full story and I'll make some suggestions of what to pick up.
So, there are some real gems in this list. I will only list software that I actually have purchased or have otherwise personally found useful after using it. This isn't to say that every piece of software isn't worthy of purchase, just that these are some of my favorites and ones that I think are worth full price, much less the discount. Most of these software companies are selling all of their products at a discount, so it might be worthwhile to go take a look.
Program that allows you to record audio from any program (including iTunes) running on your Mac. Lots of other features too, but that's the key one.
VoodoPad by Flying Meat
Wiki-like information storage system. I use it for documenting some structured information about projects I'm working on alone (use a real Wiki if you're coordinating with somebody else). Has good export capabilities
The developers may have had a bit of that whiny "Apple is giving away my product" problem, but this is a really nice piece of work for developing moderate web pages. I would still look at products like iWeb and [RapidWeaver](http://www.realmacsoftware.com/rapidweaver/index.php) (not on sale, sadly).
I don't use it any more (instead I'm using [DragThing](http://www.dragthing.com/), sadly not on sale), but it's a good program to act as an extended launcher if you don't have much screen space)
This is by far my favorite text editor on the Macintosh for power users.
A great information management tool. Works with Dot Mac syncing, has tags, lots of usefulness here
Mostly I use the free MySQL tools these days, but SQLGrinder is a nice piece of software that works with more than just MySQL. Only for admins.
RSS, Podcast, AppCast feeds. I use them to keep people up to date on my business activities
Enjoy! And, leave comments with your favorite additions to this list.