If you want to get a more sensitive microphone I would suggest the M-Audio Fast Track single XLR input audio interface. These can be had for pretty cheap used ~$85 new. The quality is good, you have input monitoring for no latency monitoring (as in you hear your voice before it hits the USB cable in the signal flow). The SM-58 does NOT work exceptionally well with this interface because the input gain has to be ALL the way up minus just a bit, if you do go all the way up with the input gain, it clips with audible distortion. This setup works, but not well enough for my liking with DYNAMIC microphones. You could go with something like this with a Fast Track: http://www.fullcompass.com/product/410682.html
Lapel microphones are great for use at your computer when you are in a relatively quiet environment. These can clip on your shirt or to a headphone cable. These can pick up keyboard noise, mouse clicks and other sounds rather loudly sometimes. This is more relaxing and more "headset" like since the microphone picks up well whether you are leaned back relaxing or sitting up straight in a more proper position. *note - there are lapel mics with a cardioid directional pattern that pick up less room noise, but the AT-831b is about the only one I see, and that's expensive.
Let me say that the SM-58 is best used when you are able to give attention to mic technique, aka within 1-3" from the microphone speaking directly into it. If you want to lean back and relax, it's better to have a mic stand that puts the mic exactly where you need it.
In short, be careful pairing a cheap audio interface with a dynamic microphone like the SM-58, you may find that another type of microphone could work better for you.
Another route to mention is using a sound card with something like this http://www.amazon.com/Zalman-Zm-Mic1-Sensitivity-Headphone-Microphone/dp/B00029MTMQ 
This is a really cheap way to get decent sound and use the headphones you want, with the heaphone amp you want. This system is flexible depending on what options you have on your sound card. If you have a digital output on your sound card that you could plug into an external DAC/Headphone Amp you're putting your money more towards the cans and not the microphone.
Another variation combining the two routes would be A. buy audio interface B. buy cheap mic like Zm-mic 1 C. get 1/8" Stereo Female to XLR male D. enjoy a better mic preamp with a really cheap mic that sounds great. Also note that USB audio interfaces don't have the "best" headphone preamps usually, so keep this in mind. They will be fine for the normal user, just not the normal Head-Fi'er.
Audio sample of Zalman ZM-Mic1: http://www.youtube.com/watch?v=M78z6l_GFao&t=3m23s
There are sooo many microphones out there, I'm sure you'll be able to make 1/8" terminated microphone + a soundcard work fine for you for less money, and I'm just as sure you will enjoy an Audio interface with an XLR terminated microphone. It's really a preference thing, and a question of will you get practical use out of a more expensive rig?
Hope this helps.
Edited by iamtwon - 1/19/12 at 5:01pm
