John asks, "What microphone should I use for podcasting? Should I look for dynamic or condenser and what models do you recommend for someone getting started?"
I believe John heard me talking about this recently on the MyMac Podcast #438 where I began to answer this question for Guy and Gaz.
For podcasting, I strongly prefer dynamic microphones over condensers. Both can work if used properly, but in the end you'll generally have an easier time with dynamics. The radio broadcast world has standardized on dynamic mics for the past handful of decades, too, and for good reason: most radio and podcast studios aren't exactly "good-sounding" rooms, and a properly-used dynamic mic naturally focuses on the signal pushed into it as opposed to condensers which tend to pick up a lot of ambient sounds, too.
The trick is that regardless of which mic you use, you'll need to employ some microphone technique. And by that I mean you want to be able to get right up close to the mic when you're talking in order to give you a nice, tight, recorded sound. Remember, your listeners will be hearing this in their own (potentially bouncy) environments, and that means you don't want to force them to listen to your bouncy-sounding room behind you, too. And if they're using headphones, they really don't want to hear your clangy room while trying to listen to your voice. The issue here is that getting up on the microphone requires you to be able to adjust the microphone's gain to compensate. You don't want to be up close only to have an over-driven sound. So you need some way of adjusting the input gain (that is, the amount of signal the microphone sends through). With most USB mics the only control you have is in the Sound System Preference pane, and while that can be good enough I tend to prefer a knob that I can adjust as I'm talking, but perhaps that's just because it's what I'm used to using.
Now that we've got the basics out of the way let's get to picking a microphone. Based on what I've said above (and to make it easy for all of us) it would seem we want an all-in-one dynamic microphone with on-board gain control that plugs in via USB. Unfortunately, to my knowledge, that doesn't exist (please comment if you know differently!). Nearly all USB-based microphones are of the condenser variety and that means we're forced to make a compromise. If you don't want to compromise you'll have to get a standard, XLR-based, dynamic mic and some sort of mixer or USB audio interface like the Shure X2u. In my main podcast studio this is the route I've gone, and I use a Heil PR 40 as my main microphone plugged in through a Tascam US-1641 USB Interface.
That said, there are two microphones that I've found over the years that work for me when I'm on the road and want to just have an all-in-one USB solution. The first is the RØDE Podcaster (US$229 from Amazon), a dynamic mic that also has headphone passthrough (which allows you to hear sound from the computer as well as your own voice directly from the mic). The one thing the Podcaster lacks is gain control — you have to do this in software and it works, but it's not perfect. Still, it's an excellent-sounding mic and I've done many podcasts from noisy/bouncy hotel rooms with no one the wiser.
The second option that I like is the Blue Yeti (not to be confused with the Yeti Pro, which is good for other applications, just not this one). Available for $93.22 from Amazon (and listing for $149) this is considerably more affordable than the Podcaster, but the Yeti is a condenser mic. However, it has an on-board gain control as well as an option for a very tight pattern that makes the Yeti an excellent podcast mic. It, too, has a headphone passthrough just like the podcaster. The Yeti has become my preferred travel companion simply because of its gain control. I don't like the sound quite as much as the Podcaster, but the convenience wins out for me. With the right tweaking I can usually make it so that most listeners can't tell the difference.
One other trick I'll mention that's helped us with Mac Geek Gab over the years: use a noise-gate (I use an outboard noise gate in the studio, and when traveling I use a software-based noise gate in Audio Hijack Pro as part of my recording chain). The point of a noise-gate is that it completely mutes your signal unless you're talking, which is great if you've got a Skype-based co-host or guests. No reason for people to hear whatever background noise you might have in your room while someone else is speaking.
Good luck... and happy recording!