Okay, you've wandered off into my area of expertise somewhat.
It really depends on your voice. I do voiceover work on the side (in addition to my day-job in radio), and have learned from experience that a mic that makes you sound like James Earl Jones on steroids will make me sound like Pee Wee Herman, and vice versa.
Admittedly, that's a bit of an exaggeration, but when you start getting into the upper-end mics price-wise, it's really different for each person. I've got about eight mics laying around my home office (including
one that cost $250), and for most of my "intended for the internet" work I still use a $25 Radio Shack mic...it just gives a better sound.
Make sure that you get a
decent mixing board to run it through (if nothing else, most mixers have an amp or a power regulator in them...this helps clean up your sound), and possibly a processor like a
Behringer MDX2600. (That's what gives you that "radio" sound). You can usually find some really good deals at
BSW.