Purchasing a Steam Game in Europe (though I am a US citizen)
Solution 1:
You can often get around the blocks that they have in place by simply contacting Steam Support (you need to register a separate account at their site) and requesting the American store, but you will then have to pay with an American credit card. I did this several times when I was in Australia and it takes 1-3 days for them to unlock your account to do so, so it may not be the best option for grabbing that game on sale.
I played the uncensored version of L4D2 while I was in Australia via this method, though I couldn't play multiplayer (I'm not sure if there were any local multiplayer servers in any case)
Solution 2:
As part of the ordering process, you'll still have to declare your actual country of residence. Whatever you enter there should be the version of the game you receive. However, I have never seen any game on Steam that was region-locked, only slightly different versions (to comply with local law, censorship etc.)
The only exception is when the game is illegal in the country you are currently in, as many games are in Germany for example.
Solution 3:
Alternatively, you can ask a friend from the US to buy a gift copy for you. That usually works fine. (There may be exceptions, but I haven't encoutered one yet.)