HP TouchPad is a fairly significant one. The big new addition is the ability to pair non-webOS phones, which will let you answer calls on your TouchPad (pairing with third-party Bluetooth keyboards is also said to be "streamlined"). It also adds a new Camera app for photos and videos, plus support for Ogg Vorbis music files, and online / offline messaging status support. Perhaps just as notably, HP is also promising "better performance" and "user interface improvements," as well as a number of other enhancements and "more robust Skype video calling." We'll be giving it a go ourselves, but feel free to share your own impressions in the comments below.
[Thanks to everyone who sent this in]
Update: We've since spent a bit of time with a TouchPad running webOS 3.0.4, and it is indeed noticeably snappier and more responsive. Receiving phone calls via a non-webOS phone also works as promised (although you can't make phone calls from the TouchPad), and the new Camera app is simple and gets the job done -- though the TouchPad's camera itself is still decidedly lackluster. Another somewhat minor but important change is the scrolling behavior in the web browser -- it now requires a far more deliberate swipe left or right to move the page horizontally, which results in far less accidental jumping around than before.