Choosing an MCU in a time-effective way
Many manufacturers of microcontrollers have selection matrix pages on their web site to support just the type of thing you are needing. For manufacturers that support various broad categories of MCUs they segment their selection matrrix pages according to these categories. Atmel for example does this according to AVR, ARM and 8051. They quickly assume that you can easily make your selection choice based on these categories before trying to drill down further. The following shows some of the choices available in Atmel's ARM selection matrix.



 







You can quickly find links to the selection guides from various manufacturers by doing a Google search with microcontroller selection guide as the search phrase. This will point to information from the likes of TI, NEC, NXP, Freescale, Analog Devices and Renesas to name but a few.