The BlackBerry enjoys an unmatched reputation as a mobile access device, and a pretty fair reputation as a phone. But even without adding new applications, it has plenty of useful functions which many people neglect. Here's five handy things I regularly do with my BlackBerry Bold (and which you can do on pretty much any operational BlackBerry).
Use it as a word processor
The BlackBerry's MemoPad function is an obvious choice if you want to make unstructured to-do lists, but you can also use it for basic writing tasks like this article. On more recent models (like the Bold) it includes a spell checker, which makes accurate editing much easier. (Access it from the Applications option on the main screen.) There's no formatting features, but that can be a bonus: rather than worry about how your text will look, you can concentrate on what it says. The only real restriction is length: in practice, you can't store more than about 1200 words in a single document. And I grant you it would suck on the BlackBerry Storm, but only because its input methods are so awful.
Not lose its mind when you travel
If you don't work for a global company, Outlook is absolutely rubbish at building a schedule, since it always adjusts times on your appointments to the local time. Fortunately, you can dodge this problem on your BlackBerry when synching with Outlook. Under the Clock/Options/Set Time screen, set Date/Time Source to Off. Your device won't pick up network time, so you'll need to change the time manually, but your appointments won't get mangled.
Work as a more than decent browser
The BlackBerry browser often takes a pounding, but if you accept that it doesn't aim to replicate the desktop browsing experience, it actually does very well. It compresses data on the fly for speedier transmission, and it's easy to navigate using shortcut keys (using F to find text on the page is particularly useful).
Sync with your desktop
Email comes to your BlackBerry over the mobile network, but your calendar and other information won't necessarily do so unless you have access to a corporate server (or use a separate software solution like Google Sync). However, if you install BlackBerry Desktop Manager, you can sync that data via a USB cable (and charge your device at the same time). Run the installer from CD if you can -- BlackBerry's site download is staggeringly slow.
Set up convenience keys for what you actually do
The BlackBerry sports two so-called "convenience keys" on the left and right. While these are set to access voice dialling and the camera by default, you can change them to whatever you like. On my Bold, I've set the left key to open MemoPad while the right key opens the browser. To change the keys, go to Options from the main screen, then select Screen/Keyboard and scroll down to the convenience key options.