you can get omni caps for the smaller condensor mics, and for the LD mics.
Omni's have a 360 pickup pattern. When used out doors where there is no hill behind you, or something that can reflect sound, they pick up a very natural sound. Get very smooth phat bass also. Also come in handy when the wind is blowing, cuts way down on the wind noise. People like to split them from 5' to 20' for more part, makes a very cool recording.