Relative Running Economy
Because Running Economy is so important but so hard to measure, I've developed this simple alternative. This Relative Running Economy is based on how many heart beats are used for the distance covered as described in Running Economy.
1 Online Calculator
Assuming you know the distance you ran, your average Heart Rate and the time it took, you can calculate your efficiency. If you know your Resting Heart Rate, enter that as well to optimize the calculation.
2 Suunto Ambit App
3 Garmin Utility
If you have a Garmin GPS, this utility will analyze the TCX files to calculate efficiency.
You can download it from http://fellrnr.com//Utilities/GarminEfficiency/GarminEfficiency.exe. Look for the tooltips that pop up when you hover over an option; they'll provide some help.
4 A more impressive alternative
Alternative Efficiency Calculator uses age, gender, and weight to calculate Calories consumed, and therefore estimate the absolute efficiency. While this is more impressive and allows for comparison between runners, it makes quite a few assumptions in the calculations. If you know your VO2max, this calculation becomes somewhat more accurate, but should still be considered only a rough approximation. Overall, I believe the simpler approach is better.