When in Maya, hit the PrintScreen key in your keyboard.
This will capture your current screen, and paste it into the clipboard. Then it´s just a matter of opening Photoshop* or any photo-editing software and pasting this image for further retouching and saves.

*One advantage of Photoshop above almost all other applications is that if you have something in the clipboard and you create a new document (File > New), it´ll create it already with the clipboard´s image size. So if you took a screencapture with a 640 x 480 screensize, then your new file will have such sizes.