As webcasters and netcasters bec0me more video oriented in their broadcasts, some prefer the aesthetics of a lavalier microphone as opposed to stand or boom mounted studio mics, such as the Heil PR40. There is no way that a lav mic will have the fidelity of a studio mic. However, lav mics are used in TV everywhere, and the quality is sufficient for the application.
The AT803 from Audio-Technica is a good choice for a lavalier mic. Since it is a condenser mic, it requires battery or phantom power. The kit includes a power pack with a standard XLR output. Street price is about $150US. Note that this mic is a wired mic, not a wireless one. Unless you specifically need a wireless mic, a wired mic is much less hassle and is much more reliable.