I recommend and use the following settings:

Textures...........High (with 1 command added*)
Objects.............Low (with 2 commands added**)
Shadows...........Medium
Physics.............Medium
Shaders............Medium
Volumetrics........High
Game Effects......Medium
Post Processing...Low
Particles............Low
Water Quality.....High
Sound...............High
Motion Blur.........Off

*If you've an adequate amount of RAM, you can use r_TexturesStreaming = 0 to turn off texture streaming, which makes distant rocky peaks look noticeably sharper.

**After setting Objects Quality to Low, you can use e_view_dist_ratio_vegetation = 31 (31 = the High value), to keep the beach rocks from popping in and out of view in front of you.

You can also use e_detail_materials_view_dist_xy = 2048 (2048 = the High value) to keep the nearby rock cliffs from looking blurry before they become detailed as you approach them. It also keeps the distant mountains from looking blurry.

Note that Textures and Objects Quality will appear as "Custom" in the game menu after applying the above tweaks. One of the best things about Crysis is all the commands you can use, though they really shouldn't cap VRAM to 256MB IMO.

If you have a GPU with more than 256MB VRAM, you can use sys_budget_videomem = (amount of your VRAM) to raise the game's use of VRAM above it's default 256MB cap. This is a very good command to use, especially in Warhead on the ice and train levels.

All you need do to make applying these tweaks a simple one time setup is make a text file named System.cfg, (without txt at the end) place the commands in it, and put it in your Crysis directory. Then every time you launch the game the tweaks will automatically be applied. You can remove or change them by editing the cfg file or remove the entire file.

Now given all these tweaks, you may even be able to go higher with the settings, like putting those at Low to Medium, but the smoke feathering of Particles isn't that noticeable on Medium, Post Processing on Medium will primarily just add blur effects, and unless you use the above commands for Objects Quality, it will actually look worse on Medium.