Are you a web developer or otherwise? If you're a web developer, I recommend (in addition to Sublime Text 2 and other apps mentioned by other people here) Sequ

Are you a web developer or otherwise? If you're a web developer, I recommend (in addition to Sublime Text 2 and other apps mentioned by other people here) Sequel Pro if you work with MySQL; TextWrangler/BBEdit for searching and editing text files; PHPStorm (Or Eclipse) for a good IDE with debugging capabilities; Keepass for password management; and 'On the job' for time tracking/invoicing.