NHS
Most sites work, although there are some odd exceptions. Here's some that I know of:
All social media is blocked. Facebook, twitter, YouTube etc
Dropbox is blocked as social / file sharing
Gmail and iCloud are blocked. I assume hotmail and other online email access are too
Almost all image hosting sites. Makes browsing the forum pretty barren!
Porn (although never tested, that's pretty much a given

)
Any "games" website. Pretty annoying if you like to read game reviews
Now the weird inconsistencies..
I can browse OcUK forums fine, however now and again a thread will time out and I won't be able to access it. I assume this is because of a keyword filter, but it's damn annoying.
All google affiliated links are blocked. I don't usually click on these but the colour accuracy is so **** poor, it's hard to differentiate between the 1 shade of pink/white they use, which gets annoying.
I'm content browsing on BBC news and the odd tech blog, (strictly on my lunch), but now and again I might search online for something and may come across some weird restrictions. Weirdly speedtest works, which I was surprised by.
I've do doubt it's monitored, so I try not to draw attention by hammering forbidden links