I have a Bluetooth Mouse (Mighty Mouse I had laying around) or any USB mouse if you have the dock will work. It can be handy at times.
Another one that I use all the time is a fine tip stylus for taking notes. The Adonit Jot is my favorite. I also have a Dagi P504, but I still prefer the Adonit. I have a 7mm rubber tipped stylus too.
For a stand, the Arkon stand is awesome, even with the TF docked it angles the keyboard a bit for easier typing.
Finally, a 32 GB class 4 or higher microSD card for movie/media storage.