Turn your iOS device (with builtin iSight camera) into a exposure meter.
Using the built in camera you can take a picture of the scene you want to measure. LightMeter will calculate the exposure for that scene and display it.
Set-up you camera to the values displayed and you will take a photo with the perfect lighting.
Using the same exposure picker PhotoBuddy does you will feel right at home. The picker allows you to change the f-stop, shutter or iso values after you measured the scene without altering the exposure.
If you use filters for your shots, you need to take them into account when calculating the exposure. LightMeter let's you set the parameters of a filter to make sure you always get the right exposure.