A couple of sites that may be of interest to you

http://thehutong.com/blog/ this is a traditional house in the centre of Beijing that runs evening cooking classes, shopping tours (they take you around the food markets and explain different ingredients etc.). I've not been there myself, but they were recommended by some one I met out there on business

http://www.chinaculturecenter.org/ is another organization in Beijing that organizes trips/classes/ general "stuff" in Beijing. Their website is terribly slow, and it's worth checking in advance if an event is still happening as one I weas interested in was cancelled previously

http://www.thebeijinger.com/ is a local events listing magazine in English - there was one lying around in my hotel lobby, and contains details of local events aimed at expats

Sanlitun (Shopping centre where the new Apple store is) has a number of western style bars and restaurants, I went there on my own and bumped into some one else there on business who was from the same small town as me - it certainly wasn't a problem striking up conversation there. In the surrounding areas there are plenty of local bars frequented by expats, but they looked more like the kind of place you'd go as a group (I was also a female traveling alone, so was more cautious of going into places I couldnt see into). The bars in the shopping centre itself are very similar to what you would find in the UK

If you want to get outside of the city, a trip to the Great Wall is recommended. Most hotels organise these, which will often go via a jade factory, and eat in a preferred restaurant etc. these mainly go to restored sections of the Wall and are busier with tour buses etc. I did a hike with this company http://www.hikingthewall.com/ and had a day hiking along the more ruined areas. You do have to be relatively fit- you're scrambling up and down unmade paths in places, and it is much more expensive than the hotel trips, but i loved seeing what felt like the "real" Wall; we only saw one other group of Westerners all day (it is a full day, collected from your hotel, and brought back there in the early evening for a day trip), they also organise over it camping trips on the Wall in ruined watch towers.

In Beijing itself the usual attractions are worth a look: the hutongs (traditional courtyard housing), the Forbidden city, Summer Palace, Temple of Heaven, Beihei park, Tiannemen square. The 798 art district was highly recommended but I didn't get chance to do that on top of all the above in 2 weekends

http://www.seat61.com/China.htm has details of trains, timetables and prices, with the new high speed connections Shanghai is only a few hours away, and there area,so over it sleeper trains to Xi'an, where the Terracotta army is.

I'm hoping to go back later this year - it's a really interesting city, and it wasn't a problem getting around not speaking anything over than English; the metro is all signed in English and Mandarin, just have the name of your destination written in Mandarin if you want to use a taxi, drivers usually don't even understand the name of a hotel from a Westerner

For decent food go to this place for lunch as they have a reasonably priced special

Maison Boulud

It is quite a bizzare experience as most locals do not know it is there. It is in a guarded compound right on Tiananmen square.

For the best duck I have ever had go to "Made in China" in the Grand Hyatt. Always book a table. But, before you go in go to the bar across the foyer and become friendly with teh bar manager. If it is the same guy he is English and will sort you out with the best table. If you have seen the "Idiot Abroad" for China he goes down a street where they are eating all sorts of crap. This is opposite Burger King outside the Grand Hyatt. You will see the red arch when stood on the steps of Buger King. Amusing to see what they are eating but I did not try any.

Get a guide and you will enjoy Beijing so much more. Our guide was called Lilly and she was fantastic. She is the highest recommended guide on trip Advisor.

Go to the Wall early and you will have it to yourself. Great for photos.

I'll be there between June 17 and 25 if you want to have some Beijing beers with a fellow PHer

Never got around to going while I was there

http://www.paddyosheas.com/

I've been before in mid-February (minus -15 degrees and 5 layers of clothing everyday!) and I'm heading back in August for a week or so. Love the city. I'm mainly bookmarking this page for the great advice you've had so far and can't add much else.

I read that the best time to visit the Hutongs is early morning if you have chance, watch the locals go about their business. I really liked spending time people watching in Beihai Park too. I stayed in a hutong close to the Forbidden City and found the local restaurants/food stalls great for some authentic grub and cheap Tsingtaos!

One thing I'd say is watch for the scam artists. There aren't many, but I almost got stung by a tea house scam with 2 lovely young ladies near the entrance to the Forbidden City. They seemed more friendly and interested in conversation in English than most people I'd previously met. I pulled a "my wallet was stolen yesterday, I don't have any money, where is the nearest police station?" and got well out of the $500 per drink tea house

I can only really echo what has been said already in this post.
There is alot to do in Beijing especially as you will be working half the time you are there.
The most useful website really is thebeijinger.com there is a 7 day guide on the website which tells you many places to go everynight (clubs/bars/eating/art/music/wine tasting).

A great place to chill and meet other foreigners would be a place called the bookworm, hosts many events such as hosting guest authors, quiz nights on a monday etc http://www.thebeijinger.com/directory/The-Bookworm

Lama temple I can highly reccomend and the summer palace will be great this time of year.
There is a cycling route in I think the latest lonely planet book which you could spend a day doing and you would get to see many different places of interest.

As previously mentioned Paddy O'sheas will be a good place to meet foreigners, as well as San Litun.

The trains in Beijing are pretty good, though some disagree. Apart from rush hour there not usually 'that' busy and its 2 yuan to go anywhere you want in the city.

Oh and if your looking for fake chinese head to the silk market, though don't pay anywhere near the prices they ask at first.

Another one who has had a few big nights in paddy o sheas in beijing! Pricey for Beijing though and food isn't great, but it's always rammed full of ex pats and foreign visitors - watched a lot of the rugby world cup there last year.

Sanlitun is a good place to go on a fri or sat night for a few beers. I also enjoyed going to Tiananmen Square and up to the wall.

The tube in Beijing isn't too difficult to use, busy but clean and tidy. Taxis are cheap, takes a while to get anywhere though, taxi drivers drive like nut jobs and I've had them start smoking when I was in the back of the cab before!

.
Yep,

been there,

And a few other Irish pubs

vette

Useful info - I'm off to China in August, including 6 nights in Beijing.

Don't have visas yet though - Anyone recommend a visa company over others? Or is it best to go to London and do it myself?

I've been in London this morning doing my visa - relatively painless. Fill up the form online, print it off, book appointment online, turn up at your specified time, hand them your form (and passport, plane ticket confirmation and hotel booking confirmation) and then come back four days later to pick up your visa.

All painless enough and you can also do it by post if you can't be bothered to go into London.