Stuff to do in London?

You might have stumbled on this post following one of my posts to twitter or brightkite. It's simple really, we are going to London soon for a short break; myself, my better half and our two boys aged 9 and 13 - I'm looking for sensible suggestions of things to do.

Hopefully things that won't cost a fortune! I've got a few ideas myself which I am posting below, most of these came from watching a program with Griff Rhys Jones about London.

Some of these I have no idea if it's possible to do at all, please tell me.

If you can think of anything, please add it in the comments, I'd really appreciate it.

Thanks!!

Some ideas :-

• Old London Stone - Canon St. The Roman centre of London (other centre is horse statue near trafalgar sq) DONE
• Any secret tunnel trips or visit the old telephone exchange underground? 
• 10:26am every day Houses of Parliament staff do a traditional walk? 
• Old Doctor Butlers Head pub, 1662. (Ale Conner's test any new beers?) DONE
• Burlington arcade in Bond St area is worlds first shopping mall? DONE
•  St Pauls Cathederal maybe. DONE
• At 10pm a toilet comes up from underground outside Palace Theatre, right side as looking at front entrance. DONE
•  Tower 42 is tallest building? doubt we can go up this.

And ideas from visitors, thanks! (updated as I get them):-

• The London Dungeons are good for adults and kids alike. http://www.thedungeons.com/en/london-dungeon/index.html
• The Science Museum has a good set of “hands on” exhibits for kids.
• The Cartoon Museum (which costs to get into) is also good if you’re interested in popular art.
• The Lyceum Tavern on the Strand is good for interesting beers. Also try de Hems in Soho for Dutch beers.
• China Town is very interesting to walk around – as are poking in to the shops & restaurants there.
• Go to the official Half Price Ticket Booth (TKTS) in Liecieiseir Square – turn up early to get the best seats.
• There’s an excellent calendar of events athttp://www.ianvisits.co.uk/calendar/events/