Coils should read about 5K ohms when cold. But, they never fail when cold, do they. To do it right, you should put them in the oven and bake them for a while to simulate a hot motor. If you don't want to bake them, then take the car for a spin and yank a coil when you get back. The warmer they get, the more they "open up" or the more resistence they'll have. Then measure the resistence between one of the terminals at the harness end and the spring at the boot end. A good coil should be under 10K ohms when heated. I've had coils that tested out at 14K ohms... they were fried. When a coil totally fails, it should measure out about the same... even when cold.
Other than that, take the car to the stealership and have them run a balance load test or a power balance test on the ignition. It should show which coils may need replacing.
