A useful script I came across because, well, I needed it recently -- my laptop's screen was dead, I was in via ssh, and I needed to check on my remaining power. Goran Larsson has written battery, which provides you command-line access to the current status of your battery.
[mysa:~] % battery long Battery 1 Battery: battery installed, above warning level Charger: charger not connected, not charging UPS: UPS not installed Voltage: 11.751V Current: 0.544A (approx 4:49) Capacity: 2.623Ah of 3.488Ah (75.2%)
You can download battery from Angry Kitchen Appliances. It's a free shell script.
On a related note, you can modify your power settings from the shell using pmset -- see man pmset for details.

