1. Logitech Solar Keyboard Folio for iPad: I hate charging up Bluetooth gear, which is one of the reasons I replaced my ZAGG Keyboard Case for iPad with this one. Apparently, you can type in complete darkness for two years once it's fully charged up. There are discreet solar cells on the back that charge up the keyboard. As a keyboard folio, it works really well. It doesn't work well as a case, so you'll have to slip it into something that will protect it from further bumps and bruises.
2. ZAGGFolio: This folio comes with a removable keyboard, and it's slightly thicker than the Logitech Solar. It comes in an array of different colors, which is definitely an interesting option. The folio looks a bit more rugged than the Logitech Solar, which is good.
3. Logitech Ultrathin Keyboard Cover: This Keyboard Cover is actually thinner than the Logitech Solar, and it will match your white or black iPad. However, I'm not a fan of the slit-based stand, which can topple if you're not careful with your device.
4. ZAGG Keyboard Case: Having used this case for about 5 months, I can say that it rarely left my home. If your iPad doesn't have any extra protection, then this keyboard case is fine. It's not the best arrangement and my model had a key that I had to tap significantly harder in order to make it work. In contrast, I take the Logitech Solar wherever the iPad goes.
5. Kensington KeyFolio 2: Velcro fastens the keyboard to the folio, which is made out of Italian leather. The folio looks somewhat sturdy, meaning you can probably forgo any extra protection for your iPad.
(Images: As credited above.)