ADB doesn't recognize my Galaxy Nexus - Win7

Check if you have installed this package in your ADB "Google USB Driver package, revision 4"; if not do it.

Another possible solution could be downloading the drivers from here: http://www.samsung.com/us/support/owners/product/SCH-I515MSAVZW

This appears to work for the Samsung GT-i9250 version too.

If you have previously installed the ADB Driver for the Nexus ("Google USB Driver package, revision 4"+) you may have to manually reinstall it.

The driver is located here:

android-sdk\extras\google\usb_driver

Simply follow your os (in Windows Device Manager -> Update driver -> Have Disc -> "Android ADB Interface"

Go to android-sdk/extras/google/usb_driver & replace android_winusb.inf with the one downloaded from https://github.com/gu1dry/android_winusb. This will add a bunch of devices, Galaxy Nexus included. Then point to that dir when installing a driver.

Make sure that you have installed the usb drivers for the phone too.
You can take a look at this guide about setting up devices for testing and see if you have missed any of the steps.