Audio-Technics AZ2020 with a USB plug is what a lot of professionals use at home. The studio mics cost $7000 but for home use with Dragon this seems to be a popular option. Your machine is not a 64 track mixing board, or whatever those things are called, so the AZ2020 will deliver all the sound quality you need.

And make sure to get a breath screen to filter out the 'pop' from your breath. These are just flat round screens that fit in front of your mic and usually cost less than $20.

And I don't use Dragon but those that do tell me there is a learning curve on the part of the program. You have to work with it a bit but when it catches on it works great.