If you would like your calls to have absolutely the best sound possible, you should use a SIP provider like onsip.com (we use them) then use HD voice phones from Polycom (the HDTV of phones such as the Polycom 335, $115, or Polycom 550). HD Voice is starting to come out from other manufacturers and is supported by many SIP gateways. The difference between a conversation between two HD Voice phones versus two regular phones is similar to the difference between talking in person versus talking on the phone. Onsip.com provides the following comparison:

To give you an idea of what the difference is, this is what an HD call with a Polycom 650 sounds like, and this is what the standard phone call sounds like.

If you would like the best sound possible from Skype, you can use the following: a Blue microphone, stand and shockmount and to eliminate "pop" a shield.  This is unapologetic uncompromising overkill.