This may be handy for ya.
Another helpful page but it's being updated a bit slower. Currently at Fizz.
Take a look at Lolcounter.com, if you want a list of counters. It will soon be launching a voting system so it will be very up to date.
Championselect is another website to help you out Not very detailed but for a nice panic situation it's okay.
I prefer CounterPicker.com
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