Seconded.
The Asus X201E/F201E (X or F depending on where they were released) are GREAT.
I have bought several of them on ebay, put in a cheap 120 GB SSD and installed Ubuntu.
Perfect Netbook. It's cheap, it's solid, very lightweight, very good screen (although glossy), decent keyboard, even has a USB 3 (plus 2 USB 2).
Battery is good for 4 hours of work or 1 movie (or 2 episodes). The power adapter is fairly small and light too.
They even look decent. Fairly good build quality too. So far none of the 6 I bought have failed.
Asus no longer produces them but they are available via ebay.
Asus originally even offered a variant with Linux pre-installed (that's how I got my first one)
There's 2 hardware variants: 2GB RAM vs 4 GB RAM.
For most stuff it doesn't matter. I get the 4 GB variants just so I can play with kvm, lxc and docker. For just browsing, email, office work the 2 GB version is sufficient (I had that on my first F201E).
The dual core centrino CPU is not powerful - but does the job.
The integrated graphics is obviously not modern gaming capable (and a request for "Netbook" involves not requiring this) - but to my surprise it does run Age of Wonders III (obviously not on highest settings). Civ 5 is usable - but with noticable lag (even on lowest settings). Stuff like Baldurs Gate obviously has such low requirements compared to modern games that it runs without problems on this Netbook. But don't bother attempting anything fps depending. Duh. ;-)
I have given away several of them and everybody loves them.
There is still demand for them on ebay.
My guess is Asus discontinued these machines (and never offered successor machines) because they were a real alternatives for the much more expensive ultra book series for most everyday tasks.
These netbooks are perfect for getting stuff done on planes, trains or in a Cafe. That's what I originally got the first one for. But I used them far beyond my original plans.
Linux has 0 problems with these Netbooks.
Full disclosure: Every nth wake-up from sleep (I never turn them off, just close the cover and put it into standby mode) wifi doesn't wake up properly - that's the only time I bother to cold boot - half a minute later it's up again.
If you need more than 4 hours of battery - just get 2 of these. :-)