One of the things that I find odd is how averse many people are to paying for software. The Mac has tons of neat applications that save time or do useful things. Here are some of my favorites:
1Password - I use this daily on my Mac and iPhone. It keeps all my passwords, bank account information, and software licenses in one place. It automatically captures the data when I input it into my browser and syncs with iCloud.
OmniFocus - I use this on my Mac and iPhone as well. It is the ultimate to do list application. The best part is setting up a universal keyboard shortcut to create a to do item from the webpage you are on. It makes it easier to close those pesky tabs. I also use the location based reminders in the iPhone version to remind me about what credit card to use at stores and restaruants to maximize my rewards.
Tweetbot - This is a twitter client for twitter power users. I like it because it keeps my timeline sync’d between my iPhone and Mac.
Adobe Lightroom and Photoshop - Adobe sells this under its Creative Cloud Photography plan. It has more features and is overall a superior photo management and editing experience than iPhoto. I got it specifically to use Lightroom. If you want to stick with iPhoto then I recommend Pixelmator for photo editing.
TextExpander - This is useful for saving typing effort by having shortcuts to paste blocks of text. I use this for frequent e-mail replies or if I have to reptitively fill out an online form.
Fantastical - This is an easy to access calendar application that lets you quickly add events using natural language.