Here are the various modern 11.6in laptops I know of.
All of these have standard memory and drives which can be upgraded. None have fantastic battery life (2-3hours for most), some have large capacity batteries available, but not all. Some have a decent support forum, others do not. While listed by price, the order often coincides with availability. I didn't list utrabooks, and by the time you cross $300 you start getting into new laptop range where some new convertibles and such start becoming available. Finding new laptops matching your criteria is FAR easier than finding older/used models that do, so I tend to keep a list of cool ones as I find them.
Low price (sub $200):
Lenovo X131E
These are cheap and plentiful. It has an 11.6in screen, however, this comes with 3 processor options, AMD, Celeron and an I3 (third generation), you really want the I3 version. I was unaware until today that it even had an I3 option. Like the Samsung it cannot be swapped with an I7, however, unlike the Samsung, these have USB 3, and are much easier to find. While I like the Samsung 300, if you are considering one, you might want to consider this instead, I would. Should support 8 or 16gigs of ram.
Samsung NP300U1A Princeton
This one I mentioned earlier, it's a nice little laptop. Second generation I3, matte screen... Only one ram slot, but can handle 8gigs. Has some actual metal fascia. No USB 3 is a downer.
Samsung NP900X1A
This is a higher priced, older version of the 300 above. It's a first generation I3 and some of this generation of Samsung seem to have Bios issues and if the bios fail, the laptop is dead. It's not common, and by now all the bad ones should be long dead, but I feel I should mention it. These are not exactly cheap, nor easy to find. While Samsungs are not that common, the bios issue may have made it worse. Again, non-upgradeable processor and this model only supports 2gigs. All in all, it's better than a real netbook, but the others here are all better choices, even the 300, which sold at half the price. On the other hand, these are a nice laptop with some aluminum on it, they were meant to directly compete with the Macbook Air.
Mid price ($200-$400):
Acer TravelMate b113
While the US version uses a Celeron, the Australian version has Celerons and a third generation I3 (possibly seconds as well). Glossy screen, typical Acer construction. I don't know much more about it. While not expensive, expect to pay a lot for shipping for an Australian version if you import it, shipping can cost as much as the laptop, putting it in what I consider mid-range. The Celerons are widely available, I3 versions are pretty rare. Should support 8 or 16gigs of ram.
Asus U24
These are very rare, not cheap, and there is a reason, they come in I3, I5 and i7 versions and support 16gigs of memory. I have been watching, waiting and bidding on these for around 6 months, I've seen 3 in that time, two needed work and even those broke $150 and parts are almost as difficult. As a result, you will want a complete one, not a damaged one you think you can repair. Warning!!!! This generation Asus often have a problem where it cannot run Win 8.1 or Win10. MS has spent considerable time on this and has never fixed it, saying Asus needs to update a drive or the bios. Asus wants nothing to do with these systems, probably because it was when they first switched over to EFI and things were a mess.
High price (Over $400):
Alienware m11x
I7, Nvidia 335m graphics, backlit keyboard, easy to find... Not cheap, and far from being slim, but it's a little powerhouse. Battery life is probably terrible.
Acer Aspire S7
These hover around $400 going up from there. They come with third generation I5 and I7, beware, there is not only a 13in version, but also a Celeron version. Personaly, I think this is one of the worst options on the list. While nice, it's an Acer, high priced, parts are non-existent.
Clevo w110er and Sager NP6110
These are insane, 3rd generation I7 (possibly lesser too) and have an Nvidia 650 graphics card in them. They also support 16gigs of ram. Now the bad... These are super hard to find, owners bought them for a reason and there is nothing to replace them. Keep in mind, all of that power is terrible for battery life, 2 hours may be a optimistic. These can still be found new ($1200+), and used ones can top $500 for a decent one and there are no parts available used... You can get new and used Ultrabooks for less and there are new small, 2in1 convertibles available for even less. Only the hardcore should really bother with these, but wow are they awesome.
Bonus 10.6in systems
Fujitsu LifeBook T580 - Tablet convertible (I.E. THICK and fragile), 1st gen processor. Usually Fujitsu are well made.
Gigabyte T1125N - 1st gen processor, probably the rarest on the list, I've never seen one for sale or in person. It's almost vaporware.
Surface Pro - If it breaks, buy another. Not a real laptop, haaaaard to upgrade.