Painkiller

Widescreen resolutions work out of the box, you just select one from the video options menu. But, you'll need to increase the FOV manually. This can be done through the console, or you can edit config.ini, which is located in <gameDir>\bin.
You can use Delphium's Field of View & Aspect Ratio Calculator .

Edit the file, and search for this line:
Cfg.FOV = 95
Increase the value according to your preference. Appropriate values for the aspect ratios are:
4:3 - 95
16:9 - 111.013676485
16:10 - 105.275347504

If you also want the screen to be hor + while zoomed in (using weapons that support zoom), look for this line too:
Cfg.ZoomFOV = 50
Increase the value according to your preference. Appropriate values for the aspect ratios are:
4:3 - 50
16:9 - 63.744671398
16:10 - 58.461499463