From: PDX (and now) London, UK
A good selection here already.
I'd add some more far flung attractions like Portsmouth, Dover, Bletchley Park and Bovington.
I've yet to visit the Bovington Tank Museum in Dorset, but may do this summer if another forumite comes (as planned) over from Germany.
There are two sites for the RAF Museum as well, one at Hendon on the outskirts of London.
There are quite a few other aviation museums in the UK. This list looks pretty comprehensive, if daunting, but you may find more WW1 centered exhibits in some of these too.
HMS Victory at Portsmouth harbor, which is pretty amazing to tour, and near to lots of modern naval vessels that may or may not be visible in the port.
The Royal Navy Submarine Museum is also there, with HMS Alliance to visit.
Fort Nelson Royal Armories Museum of artillery pieces is there as well.
Bletchley Park is a great visit.
Museum of London - a good place to go or a more thorough history of London, good ruins and views of Roman wall and fortifications, and rotating exhibits. Has photographs of London during the blitz available.
Dover is also interesting, although a bit seedy. Walks of course are amazing along the cliffs. There is a small museum that has a range of stuff on the city's importance over time, and includes a WW2 section on the large artillery battles across channel that is fascinating and terrifying.
Also, ifyou're intersested in pubs, good food, markets or anything else from a local perspective contact me directly. I'm always happy to recommend. Been here for going on 9 years, so I've learned a few tricks.
I'd also be happy to treat any forumite to a pint if you make it to London!
"Success is the ability to go from one failure to another with no loss of enthusiasm." - Winston Churchill