Best citations database

In my experience google gives you much more than others, but it is not "clean"

There are also

Those who have subscription (me not) use MathSciNet http://www.ams.org/mathscinet/

Or european analogue http://www.zentralblatt-math.org/zmath/

Also there is Russian http://www.mathnet.ru/ But it is not so developed. But it is free.

Free: http://academic.research.microsoft.com/

Free: http://www.citebase.org/

Publishing houses like Springer Elseveir provide citation services, but it is mainly within their own journals...

Apart from the ones Alexander Chervov has mentioned, there are:

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