FitBit and Jawbone are leading the industry in terms of ability and standards. These monitoring devices track steps walked, stairs climbed calories burned and they even oversee of sleeping patterings.
The FitBit allows you to keep a log of activities and nutrition. It also aggregates your data into graphic visuals to show you a colorful and easy to read map of your activity and progress. FitBit also tracks sleeping and resting patterns and can be used as as alarm. The FitBit system allows you to set public goals and share your information with friends and or family.
Jawbone comes in UP and UP24 versions. UP24 syncs wirelessly via Bluetooth (the biggest difference between UP24 and UP - which must be connected to your computer to input info). Jawbone is also equipped with sleep monitoring devices and an alarm. It also allows you to log your caloric intake and track food consumption. The Jawbone also has a barcode scanner with extensive database. The Jawbone has a less visual presentation and users can connect with friends without being tracked by location.
FitBit offers Flex - the wearable wristband ($99.95) and One - a clip-on device ($99.95) available here
Jawbone offers UP ($99.99) and UP24 ($149.99) available here