According to the IRC chat posted at inCrysis.com, Crysis is orginally designed as a trilogy, so two more are coming.

Crysis's CEO, Cevat Yerli, has revealed that we can expect two more installments of this game before the story ends. Unfortunately, he didn't want to comment any further as he didn't want to ruin the surprises. We already wrote that the first patch is coming by the end of the month, and you can read about it here.

So, there you have it: two more will eventually come. You can check out the entire transcript here.