Java TI-89 emulator (alpha version 2) by Patrick Davidson
This emulator uses the open source Pedrom by Patrick Pélissier (source available here) instead of the official AMS supplied by TI. You can control the calculator both with the buttons as well as the keyboard (the latter only if the applet has focus). This emulator does not have support for transferring files but is pre-loaded with a few of my games. If you don't feel like typing in the game names by hand, press the up arrow to cycle through the previously run commands (which happen to have been the games) to select a game, then press enter to start the game. The three included games (Platinum Edition, Mercury, and Monster) seem to work in the emulator, though I haven't tested them extensively.
There is also an version for Android phones now available. This version requires at least Android 2.2. The phone version only works properly in portrait modes and takes input only by touch. The performance will vary depending on the speed of your phone -- slow phones may run much slower than the real calculator.
If you encounter serious problems with this emulator, such as it erases 100% of the data on your hard disk, please report to me by e-mail to firstname.lastname@example.org or on IRC. However, please note that this is an alpha version so minor problems (such as erasing only 80% of your data) are to be expected and thus are not worth reporting. In the event that the emulator freezes up or crashes, there is no reset feature yet, so reload the page to restart it.
Most calculator keys are mapped to the obvious choice of keyboard input. Here are the non-obvious ones: