Popchrom is an awesome text expander for Google Chrome
Popchrom lets you set up custom abbreviations which it can then expand in any typing field. You can also edit existing entries and delete those that you no longer need. To access the options screen, just click the Popchrom icon -- which the developer was considerate enough to put in Chrome's Omnibar (instead of in the browser actions area). There's also built-in support for time and date variables.
Once you've got your abbreviations set, you expand them by pressing ctrl+space after you type (ds + ctrl+space = Download Squad). It's pretty awesome.
Popchrom currently has trouble with Google Docs, Wave, and some WYSIWG editing fields. However, it's well worth installing, even with those hiccups (which the developer is already working to resolve).