There are many threads on here that feature "software we swear by," but my list would mostly comprise Apple's included stuff. So here are the few non-Apple products I really need in my daily life:
1. Toast. I stick with version 9 since it continues to work beautifully. I like to compile music videos I've collected round the world onto DVD.
2. ACDSee Pro for Mac. I'm biased on this (see my signature), but its a powerful batch-operations tool, organiser and soon-to-be-photo editor that surpasses the lovely iPhoto.
3. Disc Cover. Use it to make my custom DVD covers. This + Photoshop = awesome.
4. Delicious Library. Organize my 2,000+ CD collection or my hundreds of books? No problem!
5. Disk Warrior, Carbon Copy Cloner and OnyX. These three tools ($90, donationware and free, respectively) keep my Mac running smoothly. If only AppleJack was compatible with Snow Leopard, sigh ...
6. Audio Hijack Pro. I listen to BBC 7 and other internet stations a lot, and want to time-shift record them. Wiretap Studio is also very good for this, but I got AHP first.
7. FStream and AOL Radio. Both excellent at storing and letting me listen to stations not offered on iTunes. FStream even records (just not as slick as AHP).
8. AppZapper. I never met a beta I didn't like, but how to clean up when you've decided its not for you? There are other apps that TOTALLY remove applications from the Mac, but this has a loud ZAP sound and I'm like 12 years old (emotionally) so I love it.
Lastly, iWork. Yes it's from Apple, but it costs extra (best $79 you'll ever spend). Pages is great, Keynote is AMAZING, and Numbers is very cool but I'm not much of a spreadsheet person (but when I need it, I need it to look good, and Numbers delivers on that in SPADES).