Quasi,
This information might be covered elsewhere, but this was my experience bringing over my cat. Everything went very well. Make sure to check with the airlines regarding international (actually transatlantic) in-cabin pets before making your flight arrangements. You will want to bring your cat in-cabin in one of those mesh carry-on pet bags. It's really not a big deal - just stop feeding him/her 16 hours or so before leaving, then provide your cat with a small amount of water the morning you leave, and give some dry food during the flight. Most vets recommend that you do not give tranquilizers, as the reaction can be unpredictable. Also, you will want to keep your cat in a harness and leash at all times - you must take him out of the cat bag and walk him through security. I had to do this 2 times and the cat was quite scared but I had a good grip on him. You will also need to forcibly shove him back into the bag after this. Do not try to be nice - just fold him up and stuff him in the bag. I am serious, as when I tried to be nice with him and get him to go into the bag on his own, it took over 30 minutes.
I flew over from the US in August, and the only airline that I found with in-cabin international/transatlantic pets was
Lufthansa. Some other airlines (Delta, US Air, I think I called about 5, etc.) permit in-cabin pets for flights within North American and the Caribbean, but not to Germany, so make sure you ask about Germany - call and speak to an airline representative just in case and don't just go by what is on their website. I booked through Travelocity and then called the airline to book the cat, but only after asking the airline rep if in-cabin pets were still available on the specific flight I was planning on buying (after I located the flight # but before purchasing). Other airlines permit cats as cargo, but that means that your cat is shipped in the cargo compartment and I did not feel comfortable doing that. But, and this is very important, some airlines that do permit cargo pets have temperature restrictions (I think only in the summer, but maybe also if it is very cold). I was concerned I would not be able to bring my cat because at 85 degrees the airline will not permit cargo pets, and it was certainly over 85 degrees in Texas in August. If the temperature restriction is in effect, then you would be stuck at the airline counter with no way of brigning the cat.
There is no quarrantine in Germany - check out the links on the other pages here to get the forms. I'm not sure about the quarantine if you fly through London, but I did not want to risk that, as I found conflicting information about that. You will need to get him microchipped with a "Euro chip." The Euro chip is just a normal chip but unlike in the US it has 10 digits or something. I had to order one on the Internet, and I took it to my vet to have it inserted. Also the rabies form. I had no problem, but I did end up paying the airline charge for each leg of my flight, and the counter person at JFK was quite thorough in the inspection of my forms, etc.
Please PM me if you have any other questions. My cat was quite the trooper and he is now settled in quite nicely here.