...well sort of. I'll be working in London for two weeks and I'd like to visit another country or countries over the weekend. I'm looking for interesting places that are easy to get to from London. I've been to France, Germany, and Switzerland already so I'm looking to go somewhere else. Suggestions?
My friends and I spent two and a half months back packing through Europe last summer, and from a sightseeing perspective, Rome was definitely at the top of the list. The Cathedrals alone are worth the trip (and that's not even including the Vatican, the Coliseum, the Galleria Borghese, etc.). For your buck, Rome has the most bang. Florence is really lovely too, everyone should see Michelangelo's David sometime in their life and the river running through the city is amazing at sunset. I also really liked Salzburg. It's clean, beautiful, and relatively uncrowded. The night sky especially is beautiful. After being in Houston for six years I'd forgotten what a sky full of stars looked like. A lot of people will probably suggest Amsterdam, but unless you're into the pot culture, I think there are a lot more cities with more to see (though the Van Gogh museum is amazing). Also, if you have a chance to go to a big time soccer match, be it in England or elsewhere, take it. We saw Roma's last match of the season and it was awesome.
So you want close to London for a weekend getaway? Go to Scotland. Go to Wales. Go to Ireland. I drove from London to Neath, Wales, which is west of Swansea, several years ago. It was gorgeous....easily one of my favorite drives anywhere, ever. In my opinion, a LOT of people go to London and seem to think that's all there is to Great Britain. Not that you're one of those folks, but my simple point is that all of the British Isles are fun with lots to see and do. Go to Glastonbury Abbey and Bath, both in Somerset. Tintagel in Cornwall. Stonehenge, etc. if you decide to stay on the main isle. A lot of these sites are related to Arthurian legend. The legends may or may not be real, but the sites are all very real and are very impressive with lots of history. Great Britain and Ireland are amazing in general.
Prague and Budapest are pretty awesome if you want to travel a bit of a ways. EasyJet flights are pretty cheap, and then you can find places to stay in both of the cities for not too much. Prague is the most beautiful city I've ever seen. Not sure where you went in France and Germany, but if you haven't spent time in Bavaria or in Provence, you can easily spend a leisurely week in both of those areas. My wife and I rented a car and drove around a week in each of those areas and had an awesome time. Bavaria is my favorite region in Europe. We went to Munich, Lake Prien, Rottenburg, saw Ludwig's castles, and had incredible food and beer. Provence is just as beautiful, but it's French cafes vs. beer gardens. Aix and Nice are great places. You can't go wrong with Tuscany either. Amsterdam and Bruges are pretty fun as well...even if you aren't hitting the coffee shops.
I just reread your post and realized your time constraints. If you only have a weekend, go to Edinburgh. That city is awesome!
I second italy, ireland, and germany. sooo amazing!!! if you haven't been to bern, you should go to switzerland again.
If you are a Disney fan by any chance, then consider Disneyland Paris. Not very far if you take the train across the channel.
You can go to Brussels, it's just 2h by eurostar from London. Then you can go to Antwerp, Bruges, Luxemburg, Amsterdam, The Hague. Lots of places are 2h and less from Brussels by car or train.
Thanks to all for the suggestions. Flights to Rome seem reasonable. Otherwise Ireland/Scotland seem easy.