I bought the Targus case when I bought my A500 in July. It works great for standing the tablet in three different landscape positions. However, it also adds significantly to the weight and bulk. It does help protect the screen when closed, and could surely help protect from damage in event of a drop. Last week I bought the Acer portfolio cover. It is much lighter, but a tradeoff is it isn't as easy to stand up as the Targus case. It also blocks the microphone, but that can easily be rectified by simply punching a hole in that location (and applying other velcro tabs in another location to keep the cover closed).
I bought a wet application screen protector when I bought the tablet, but got fingerprints all over it and ended up ruining it when trying to remove and reapply. Since then I discovered a much cheaper version on Amazon.com that is easy to apply and works well. The brand name is Posrus. Shipping is very quick. I also installed one on my wife's Toshiba Thrive. (Both bought separately with shipping costs for each were still less than the one I originally bought at Best Buy and ruined because of how difficult it was to apply.)