You might also like to try the Crowne Plaza Hotel restaurant in Shoreditch High Street. The view is extensive though not particularly beautiful. http://www.crowneplaza.com/hotels/gb/en/london/lonsd/hoteldetail
Relatively new, and so far surprisingly unknown given its amazing location, is the Madison restaurant and cafe on top of One New Change, completely with great views of St Paul’s Cathedral.
Strictly speaking, there are two venues here: a cafe, currently under refurbishment and with decent views from inside, and also a restaurant/bar, with lovely comfy sofas next to windows and fantastic views.
Although I was there on a sunny weekend during holiday season, there were no other members of the public there (aside from the Peruvian Ambassador, of course*). Also in short supply were any five pound bank notes, resulting in amusing scenes of the (very friendly and helpful) staff searching in turn through their own wallets in an attempt to resupply the cash tills.
The place comes with two added bonuses – a roof terrace viewing platform with great views across London, including of The Shard, and also the lift up to it being a lift with a view too:
Alternatively, especially if you are visiting with young kids at a quiet time, try the escalators with their two-speed accelerating thrills.
* Hello, Mr Fenwick!