Type of mic to buy

I am part of an organization that gives talks to different types of groups. Sometimes it is in a small group setting. Sometimes it is in a large hall or church that has a sound system with a wireless or chorded mic. We need a mic that can either feed somehow into a laptop for recording, or preferrably to use with a handheld digital recorder similar to an ipod. I would most like to find a lapel type of mic that would plug into the digital recorder. I need it to record the speaker's voice without getting a lot of background noise or white noise. It will sometimes also need to be used along side the sound system mic. We are wanting to record high quality audio for podcasts. I am the webmaster but I have no knowledge of of audio equipment. I have read a little and so far I am thinking I need a unidirectional mic. Is this correct? I have been told that our organization does not mind spending the money necessary to get a good mic or recording equipment.

Any advice on type of mics or specific mics would be greatly appreciated.

Thanks,
Laura