Skip the Line: Vatican Museums Walking Tour including Sistine Chapel, Raphael's Rooms and St Peter's
The tour guide was excellent - very knowledgeable and personable. Bring a water bottle because there's no where to buy bottles inside - there were one or two fountains inside VC to fill your bottle with potable water however. We aren't catholic but the art, buildings and architecture, the history etc. was amazing and very interesting. We were almost late because we didn't realize the tour started at the VATICAN MUSEUM entrance - our fault - but we had a hard time finding it once we did realize this. So pay attention to the starting location.
We aren't that into art - so we weren't too thrilled but we still wanted to see it. In fact the only impressive thing there was Michelangelo's David. The rest of the art was not that interesting to us - but I know nothing about art. If you don't either - then you're probably not missing much. And the skip the line thing wasn't that big of a deal. There didn't seem to be much of a ticket buying line when we showed up.
Excellent value - I would absolutely recommend this. It's almost a requirement if you're visiting all the major attractions. We bought the travel card which includes buses and the metro in Paris - but we didn't use it once. We stayed near the opera house and we're in our late 20's so we walked to all the major attractions we wanted to see: Notre Dame, the Louvre and Orsay, Latin quarter, the arch, Eiffel tower, etc. It's all walkable and you experience more of the city if you do this. Especially if you like to shop or want to catch a cafe - then walking lets you stop when you want. Note that if you have this pass - you can skip the ticket-buying line to the Louvre and there's a side-entrance that didn't have a single person in it. Still have to go through security but that was quick. The ticket line was real long. I would highly recommend the pass - the travel card maybe only if you want to take the metro.
London, United Kingdom
I would absolutely recommend this - in fact it's nearly a must if you are planning to see all the major sights. It was handy b/c we came across a few other attractions we weren't aware of i.e. the WWII Churchill War Rooms museum - and were able to get in free with the pass.
Definitely get the travel card too - it's extremely convenient in London. Things are definitely more spread out in London than they are in Paris (we literally walked all over paris and didn't use public transportation once) so we used the bus system extensively. The London Underground is a bit cramped - so we didn't use it - but the bus system is nice and very well done.