Being a long time user of the software I'm delighted that its available for Aperture. Admittedly, with some of the newest pro DSLRs the high ASA noise levels aren't too much of an issue, but once in a while you're forced to get rid of some noise and in my experience, Noise Ninja is the best and most subtle looking out there. They have a trial version, so give it a go!
Looking into the plug-ins scene, there appear to be more than 70 now available. Whilst some are a bit gimmicky, there are certainly a good number that are very useful.