What are the lightest laptops ?

It might sound like a stupid or unusual question but I would like to know what are the lightest, yet somewhat high-performance laptop currently on the market. I'm a university student and I've been stuck with a bone disease for quite a few years now. It got to a point where carrying my current Dell notebook is just too heavy for me.

And when I say light, I mean like, very very light. I know about apple and their Macbook Air line but I've never been a fan of Apple and I think their products are just overpriced for what they offer.

Here's a quick checklist of what I need (or don't need):

- Super light
- 1 200 $ is as high as I am willing to pay
- Won't get too hot
- The keyboard must be of very good quality and comfortable as I type a lot and my hands are affected by the disease.
- Good trackpad
- Powerful enough to be quick and responsive.

- I do not need a lot of HDD (or SSD) space, I am perfectly comfortable with anything between 128gb and 500gb.
- I do not need a DVD-drive
- I won't require the laptop to play high-end games on max, although I do like to play a few minutes of Diablo 3 here and there between classes, and I can live with playing on medium.

I think that's pretty much all of it. I don't have a favorite brand name for either the CPU, GPU or the laptop itself. Thanks everyone !

Edit : I forgot to mention something ! Anything bigger than 15" or 15,6" is too big for me. The ideal size would be somewhere between 12" and 15" I guess.