Being a Mac user I love applications. Here are some of the tools I use religiously - both hosted and local:

Basecamp - Project Collaboration
Kashflow - Online Accounting / Bookkeeping
Coda - Website Development
Tweetdeck - Twitter
Skype - Cheap phone calls
Skitch - Great image screengrabs
JungleDisk - Online data storage
Freshbooks - Billing and Invoicing
1Password - Password / Login Storage
quicksilver - fast hot-key app to everything in the world

Open Source endorsements:

Drupal - CMS
Open Goo - Online Office
VLC Media Player - Entertainment

Other

iStockPhoto - Affordable Stock Images
Macspeech Dictate - Voice recognition/dictation software Mac