I've used three so far ...
The first one (shown on the right in limey green) is called the Hard Candy Bubble Sleeve and it's great when storing your iPad or iPad2 when not in use. Toss it in a backpack or purse and your iPad is safe while nestled inside this molded EVA-foam case. The downside is that protection ends when you remove your iPad for use.
The second one I've used (shown in red) is known as the Hard Candy Candy Convertible. This case is made of a faux nubuck material and it stays on your iPad while you use it. It's professional looking design includes a flip cover that tucks into the back for two optimal viewing angles. The overall design is slim making and it doesn't added a ton of weight to the unit. While it does pad your iPad a bit, it's still not the best bet for the littlest of household iPad users. It's a perfect "take to the office" option though.
The third iPad case I've used (shown in black) is known as the Gumdrop Drop Tech. This is the case I typically use when my 3 year old twins are taking control of my iPad. It features a design that allows for shock absorption, drop protection, and overall ruggedness. The design features multiple layers of protection including a replaceable, snap-on integrated screen. The downside is that it adds a little extra weight and bulk to the unit, which is why I take this case off when I'm the only one that is going to be using it. With that said, I'll take the bulk it adds any day over a broken iPad.
Cases to watch for in the future: I've seen a few cases "coming soon" that will combine high levels of protection with some great innovations perfect for iPads being used by busy families. One such case said to soon release is the UZBL iPadFlex. It's website shows a protective case that can be "strapped to your hand, carried over your shoulder, fastened around your car headrest, mounted on a wall, attached to tripods, or connected to accessories that can allow your iPad to be mounted on a desk, workbench, chair, or most anywhere."
Disclosure: I was provided with some of the cases mentioned in the above round-up, however all opinions are my own.