How much do you want to spend, and where are you at (so I can steer you to the right places to get this equipment)? I have an omnidirectional mic here that I spent close to $1000 on, not including USB or Firewire interfaces, but probably it would be overkill for what you're doing!

First things first, more information on what you're planning to do would certainly be helpful:
Can you describe the room you're recording in? How live/reverberant is it? How big is it? How are the people being recorded going to be arranged within the room? You mention chatter, what kind of chatter? How were you planning to feed the output of the microphone into your computer? What operating system are you using? In the past, what was it about the recordings that made them difficult to understand? Perhaps you might want to consider renting some equipment instead of buying it?