Take a look at http://www.zagg.com/.
I used the invisible shild intended for Apple Ipod touch for my Aventura. It is longer in its size then the Aventura screen. Width is a little wider then the Aventura's one. I cut the upper and lower edges leaving it -half a milimeter longer at each side.
The attaching procedure requires the use of a special solution. By applying the minimum solution and working with absorbing tissue at the screen edjes (to eliminate risk of wetness penetrating the screen) I succeded to attach the shild to the screen.
The results are amazing. There is no ability to see that additional protecting layer exists on screen. Some small scratch disappeared and can't be seen. Furthermore, the touch screen get a spongy feeling when using a stylus and seems to become more sensetive with or without using the stylus.