The Material design website mentions a new Toast-like element called a Snackbar: http://www.google.com/design/spec/components/snackbars-and-toasts.html
The Android L preview SDK documentation (sorry can't link since it's only downloadable) doesn't have any mention of Snackbar in the classes list or as a modifier in the Toast class documentation. Am I missing something obvious or should I build my own Snackbar.java?
Update 2015-05-29:
Google released a Design Support Library which includes a Snackbar and other Material Design widgets.
The Snackbar lib mentioned in the original answer is now deprecated.
Original answer
I'm sure Google will eventually include it in a future SDK, along with a Floating Action Button that is also missing in the preview SDK.
As @friedrich nietzche pointed out, I implemented a library to include a Snackbar in your project.
https://github.com/nispok/snackbar
Hope it helps!