Word Processing/Spreadsheet/Database
There is Microsoft Word for Mac (possibly a good choice because you know the app)
Mariner Write has been around for many years, and the keep improving it. It costs less than Word and is totally compatible with it.
There is also Open Office, which is free and eminently downloadable here.
Open Office was created as an alternative to Microsoft's Office package, so it also contains data base and spreadsheet.
Music Player (right now I've got iTunes & Play)
For mere playing, iTunes should be is all you need.
Audio Editing software
Audacity works very well and is a free download here.
Picture Editing software
While you can do some of that in iPhoto, I recommend (and use) Adobe's Photoshop Elements. The new version is great.
Video editing/burning software
For normal video editing, iMovie and iDVD are flexible and easy to use. In fact, one can do amazing things with those apps.
Burning is inherent in the Mac system, but you can do much more with Toast Titanium. Look for the periodic special deal.
I highly recommend that you get the iLife package, which contains iPhoto, iMovie, iDVD, and Garage Band (create music). There is a new iLife coming soon, the latest is iLife '09,but Apple is dropping the year tag. You will find the best price for this package at Amazon—go to the "new/used" offers and save about $25 .
I hope this is helpful.