I am trying to save maximum energy for a certain embedded Linux application. Currently I am using Raspberry Pi. But it looks like Raspberry Pi doesn't support Suspend to RAM. What alternative embedded Linux platforms can support this feature?
You should look to side of Live CD.
Often there is exist such option: "boot to ram".
You can boot from live cd or usb stick, even from hard drive to RAM. In this way, your system need no suspend to RAM, it is "installed" in RAM. No disk required.
You can save much disk requests and increase whole speed of you linux in more than 5x. But you will lose your RAM.
If you are rich of RAM, e.g. >2Gb, this is perfect solution for you.
Read "man live-build" and "man live-boot"
You can have a look at the beaglebone black: http://beagleboard.org/Products/BeagleBone%20Black which is not that expensive and can suspend to ram just fine.