There is a version of MS Office for Mac, (Student & Teacher edition is cheap) that will cover your word processing, spreadsheet and presentation needs.
However, there are alternatives to paying MS anything. OpenOffice and NeoOffice are two programs that can create and open MS Office files. Both are free and worth checking out.
Apple has an application call iWork which contains a suite of programs, Pages, Numbers & Keynote, which do the same thing. It's not free but it's cheaper than MS Office.
Video editing. You already have all you need on your new mac to start into video editing. iMovie and iDVD will do you fine. If you want to go the "Pro" route at sometime in the future, Final Cut Express or Final Cut Studio is used extensively in the movie industry.
Music Software. This depends on what you want to do with your music. Store it, play it, catalog it & sync it to your iPod, then iTunes (already on your computer) will do fine. It will also convert tracks to different formats. It is not really an audio editing suite though.
Garage Band, already installed on your computer, is a good piece of audio software but may not be what you are looking for.
Audacity does about the same as Audition but does not look as pretty. Logic Express or Logic Pro, from Apple, are very good.
Photos. iPhoto, already installed on your computer, is a great way to store, organize, edit and share your digital pictures.
OK, so far we have not found any software that you need that is not already on your computer, the need for Windows is fading.
Check out what is already there, iTunes, iMovie, iPhoto, iDVD, GarageBand, (collectively known as iLife), you may have a trial of Pages, Numbers and Keynote (known as iWork) and maybe a trial of Office.
Avoid that, they are trying to sell you the full price version.
When you find something that you positively cannot do on your Mac, post back to these forums and you will find that you probably can.
Download OpenOffice and see how you like it. You can always uninstall it.
Good Luck
P