Here are a few every-day useful apps I have picked up over the years:

Mountain Lion Cache Cleaner http://www.northernsoftworks.com/mountainlioncachecleaner.html
Carries out all the maintenance tasks you could want for your mac simply and easily; including virus scanning.

Cloudmark DesktopOne http://www.cloudmark.com/en/products/cloudmark-desktopone/index
Intelligent spam protection tool for your email that uses several techniques including blocking emails that other users of the program have blocked. Works with Mail app and

Little Snitch http://www.obdev.at/products/littlesnitch/index.html
A simple tool that lets you allow or block incoming/outgoing internet communications from your applications separately for greater security.