I have a new Audio-Technica AT2020USB+ mic. Windows 7 Pro.
It's plugged in, it's working, I tested it in the Logitech video app (which is now closed), It is set up as my default recording device.
However, when I open Sonar and go to Track 1's Input Selection Window, it's not there!
Please help!

USB mics are configured differently. From the user guide:
 
"Set your Output Driver to
<name of your sound card> (WDM / KS). Set your Input
Driver to your USB microphone.
You may also get good performance by using WASAPI."
 
Also see: http://forum.cakewalk.com/Technical-help-USB-Microphone-woes-RESOLVED-m3218908.aspx
 

have you gone in to preferences and selected the AT mic under devices ?
 
Audio-Technica USB audio products do not require any special drivers from Audio-Technica but rather are designed to be “plug and play” by utilizing an operating system’s USB Audio CODEC driver.
 
what driver mode are you using this mic in ?
and do you have a soundcard, or using onboard ?

I switched to MME and it showed up. I tracked 6 minutes of perfect voice audio!
Is WDM better than MME?

bilo06
I switched to MME and it showed up. I tracked 6 minutes of perfect voice audio!
Is WDM better than MME?

you still didn't really answer my question about your soundcard so I cant really tell you what mode you should be running.

WDM just defines the way a driver presents itself to Windows. WDM/KS (Windows Driver Mode/Kernel Streaming) audio is a low level access comparable to ASIO and is absolutely better than MME. MME has been around since before Windows 3 and is usually going to give you the longest latencies of any of the available driver modes. If it is working for you then fine, if you can get to an ASIO or WDM/KS driver that will be better on more demanding applications.
 
http://promos.chooch.us/archives/479
 

it all depends on what your using for a sound card. hence the reason I asked.
I don't want to give you information based on my best guess.
 
You have three Modes to Choose from: MMe, WDM and ASIO.
For best performance it's important that you choose the proper driver mode for your audio hardware. Here are some common scenarios:
If you are using the sound card that was shipped with you computer choose MME as your driver mode.
Choose WDM or ASIO if you are using an Audio Interface or sound card that you purchased or installed specifically for use with Audio applications such as SONAR.

Almost all audio interfaces/sound cards designed for audio applications can use either ASIO or WDM drivers. Either mode provides low latency and stable performance. If you're sure about your audio card. try both setting or check with your hardware manufacturer about which driver they recommend 
 
https://www.cakewalk.com/Support/Knowledge-Base/2005261/Choosing-Driver-Mode-in-SONAR

Thanks for the info! Very helpful.
I have a Line 6 Studio GX for my external soundcard.

bilo06
Thanks for the info! Very helpful.
I have a Line 6 Studio GX for my external soundcard.

doesn't the Line 6 Studio GX use ASIO drivers ?

USB mikes are sort of usless because they don't have XLR connectivity. So they use Generic Audio Codex which will talk to many windows apps but not to Sonar ( or most other DAW's) They probably work fine on Macs, but Windows is far behind in generic audio drivers. Hi latency and tracks won't be in sync etc. 
Take it back and buy one with a profesional XLR connection. THen you'll have a mike that can be used for everything,, not just podcasting. 
 
If you wish to sing into Sonar you will need an audio interface with XLR input anything else is sub standard.