The coolest thing I saw was just 2 hours outside London...jump into a train to Portsmouth and visit the HMS Victory. It's amazing how big this thing is, and it's made almost entirely of wood.
The British Museum is also very recommended.
What's also really cool (especially since you're an env guy Wahlgren), St. Paul's cathedral. One of the most beautiful churches ever. Make sure to climb up all the way to the dome so you can look down to the inside (then climb some more) and look down at the outside.
I heard you can also get a guided tour thru some old war time tunnels of the tube - I never got around doing that, but it sounds interesting.
If anyone cares, I can give travel trips for Oslo, Austria, Beijing, Shanghai, South Florida, little bit of London
LoTekK: Singapore...I might visit eventually. When it's not sooo hot