Wow, they're beautiful pictures! I'm actually booking a trip there next weekend myself, and I'll be taking my action figures with me :)

Do you have any must-see recommendations for Paris? I hope 3 days will be enough!

You have a nice (free of charge) view of Paris from the Samaritaine, a department store opposite of Pont Neuf (which is despite of its name (new bridge) in fact the oldest bridge of Paris).
http://www.online-reisefuehrer.com/europa/frankreich/sehenswuerdigkeiten/aussichtsterrasse-kaufhaus-samaritaine-2.htm
If you are there take a look at the bridge (Pont Neuf) as well. Opposite of the statue of Henri IV (which is on the island in the middle of the bridge) you should enter Place Dauphine. It's a triangular 'square' and suddenly a very quiet place. Very lovely.

And did you know that there's a small Statue of Liberty in Paris?
http://en.wikipedia.org/wiki/Replicas_of_the_Statue_of_Liberty

I loved Sainte Chapelle and the Jardin du Luxembourg.

Anything you can recommend in London? I'll be there on a long weekend by Mid of July.

Ooh, thanks for the tips!

You should see Trafalgar Square for sure, it's a beautiful open space and right in front of the (free!) National Portrait Gallery/National Gallery. In walking distance from there is Leicester Square, Covent Garden, and Piccadilly Circus. And I assume from your interests that you are a fellow geek, so Forbidden Planet (http://www.forbiddenplanet.com/WhereWeAre.html) is definitely worth checking out. Big Ben is also worth a visit, and Westminster Abbey is right next to it (admission to Abbey is 10 pounds, and I think it is closed Sundays for worship). And make sure to see the British Museum! Their exhibits are vast, and they have the Rosetta Stone.

Having some sort of street map helps a lot; London is a fantastic city to get around on foot in, and a map helps you get to where you want to go right away (the streets can be confusing the first few days). Even many native Londoners carry street atlases because there are so many random side streets!

Never a visit to London without the Forbidden Planet! *cough*

I think the Centre de Pompidu and the Louvre might be fun for you. I also recommend Jardin de Luxembourg. And maybe a cemetry ;)