Gadwin PrintScreen is one freeware provides all the features you require from a screen capture application. The is interface is quite user friendly, different shortcut keys can be assigned. Version 4.3 adds multimonitor support, improves Windows Vista compatibility, and date/time stamp feature.
It sits in your System Tray, and you can set a number of options. When you hit print screen (or whichever button you specify), you can choose to save the screen directly to a specific folder. You can also choose to save just a window, or a specific area of the screen. The application also gives you the option of sending the screen capture directly to your printer or as an email, and it will even automatically resize the picture to specified dimensions. You can select the type of image you want to save.