Based on what you've posted here you'd need a GeForce GT 540M graphics card to support your request for: crysis 2 medium settings 40-30+ fps.
Something like that is going to run you, minimum, $700 on your credit card.
Looking at the graphics card performance - how low are you willing to go? Pick a graphics card that is the lowest you'll accept. http://img820.imageshack.us/img820/4527/ss049u.jpg
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