Well.. the BEST spec would be the fastest and newest hardware on the market though I doubt that is what you meant. I'm not quite sure what the minimums are but if you do a forum search or google search i'm sure you could find a few ideas.
As for what I use.... i'm running a i7/GTX470 and the game runs without a single hitch.
For Warhead any good dual core cpu like the phenom ii x2 555 or the core 2 duo e7500 is a must with at least 2gb ram.As for the graphics these are what I think are required for 1440x900 resolution at the least:
medium settings(called mainstream in warhead menu):9800 gt/ hd 5670/ hd 4830
High settings(called gamer)without aa:GTS 250/hd 5750/hd 4850;with aa:GTX 260/hd 4870/hd 5770.
Although note that at these settings you would get an average of 30 fps which is very good for crysis.But in other games you might get what you want and you might have to turn down details in the snow missions where it gets laggy