Do you have a smartphone? If so, no matter what platform you use, there are lots of free apps that can help you become more productive.
Dragon Dictation: Dictate reminders to yourself & e-mail, Facebook, or tweet them...not recommended for use while driving. iPhone/iPod Touch, Blackberry
Dragon Search: Use your voice to search Google, YouTube, Flickr, Twitter, iTunes & Wikipedia. iPhone/iPad/iPodTouch
Evernote: Create text, audio & picture notes. iPhone/iPad/iPod Touch, Blackberry, Android, Palm, Windows Mobile
Google Mobile: Access Google Docs, RSS feeds, News, Maps, etc. Includes voice search. iPhone/iPad/iPod Touch, Blackberry, Android, Palm, Windows Mobile
ListPro (free for 30 days): Use 30+ templates to create lists that can be sorted by category, date due & priority. You can also e-mail yourself reminders. iPhone/iPod, Windows Mobile, Palm
Do you have any recommendations for killer apps--free or otherwise? Post them in the comments section!