There's actually plenty of documentaries showing how they (humans) make the crop circles. Just very creative artists if you ask me. Now, I believe in 'aliens' but to go as far to say they'd come and make a few crop circles seems a bit too far fetched for me. Of course, feel free to think what you like, but I just can't see the reason why they'd do it. Unless it was in fact for the lulz, if so, I like them already. Good sense of humour gets you far!
Personally, I find it bullocks. They used to say lightning and storms were the gods getting angry, we know better now. Not to say I'm close minded, but I am sceptical nonetheless. I won't just jump to conclusions everytime something slightly out of the ordinary happens.
But yea, I saw a documentary on National Geographic about it recently, a bunch of guys making crazy crop circles rather fast.