have you checked this one - http://interface.khm.de/index.php/lab/experiments/arduino-frequency-counter-library/ -
BTW, can you define more details about your needs?
Is it a freq counter of dicrete events (0..5V) or determine the frequency of an analog signal?
What is the working range ?
1 - 1000 Hz
1 - 1.000.000 Hz
What is the duty cycle of the pulses?