SysMon is a complete iPhone/iPod Touch/iPad monitoring app, that lets you know about the current memory in use and free [ Memory here stands for Random Access Memory-RAM, devices has the limited RAM from 128 mb to 512 mb ].
This app also lets you know about battery level, processes running in background, disk information that gives you information about total disk capacity and total disk space used and available, cpu load percentage and device information such as device name, model, IP address, MAC address, your device's unique id and more...