Hi! I am new to this forum and wanted a little bit of help.
I want to purchase a new laptop for daily use that includes Internet surfing, watching movies.
Main things which it should have: compact, light, has a decent battery backup. Screen size: 11.6 inches.
I am confused between Intel Pentium DUAL Core, Intel Celeron Dual Core, Intel Atom. Which one of them is better and why?
Other specs: 320/500 GB HDD, 2GB RAM, Win 8, NO Touchscreen.
Brands: Lenovo, Asus, HP, Dell.
So recommend me some models? 

P.S: I have a tight budget.
Pentium Dual-core is usually better than Celeron Dual-core, although sometimes the Pentium and Celeron Dual-cores are the same just different naming. Generally the Pentium Dual-cores will perform better

As far as RAM goes you will want 4GB minimum, as well as I would look for a laptop that does not max out at 4GB but can take say 8GB or more.

320 or 500GB HDD all comes down to if you will be storing large amounts of data at all. The HDD speed is something you might want to look into if proce difference is small between the 320 and 500. I would go with a 500GB.

Recently I bought an ASUS Laptop with Celeron M1000 Dual-core 1.8Ghz and 4GB of RAM with 320GB HDD which came with Windows 8, and it was $279.99 at newegg. http://www.newegg.com/Product/Product.aspx?Item=N82E16834231360

I bought this here because it was cheap and light weight. * This model does not come with a optical drive, but I had a external USB DVD-RW drive.

I would avoid an Intel Atom CPU because while battery life would last a while with a low power draw CPU, from personal experience with a Intel Atom Netbook, streaming video is very bad with it. That is one of the reasons why I bought this cheap replacement to my netbook.

If you can AFFORD a Core i3 CPU system, I'd go with that. But if your not going to game on this system and just going to use it for watching movies a brand new Celeron M1000 Dual-core or better or Pentium Dual-core is the way to go.

I have since downgraded my ASUS laptop to Windows 7 64-bit Home Premium though because I had some bugs with mouse controls in games with both Windows 8 and Windows 8.1 . I downgraded to Windows 7 and this fixed the mouse control issue. I play World of Warcraft on this laptop with no problems on Normal Graphics settings with the integrated Intel HD Graphics. My framerate is 25-40 fps. It also plays netflix, hulu, crackle, and other streaming content with no problems. *Also this laptop has a HDMI connection and so I can plug the laptop into my large screen TV and watch shows/movies, or even play games through 36" TV.

I havent had any problems with this $279.99 laptop other than the mouse control issue with Windows 8 and Windows 8.1 thinking upgrade to 8.1 would fix it and it didnt. I had a spare Windows 7 KEY from a 3-license family pack that I used to downgrade to 7 on this laptop.Thanks a lot bro! It really helped me and I am LOOKING forward to buy Asus now.