Around the new metro stations of Hills Showground, Norwest, Bella Vista and Rouse Hill are some good cycling trails.
The first follows the new cyclepath that follows the train line from Bella Vista to Schofields Station on the Richmond line. This trail can be combined with the paths through Crestwood, the M7 Cycleway and even the long run down from Windsor.
The second video heads down the Smalls Creek path and returns up the Windsor Rd path. After that the video goes through Tory Burn Reserve and all the way to Westmead. The rider featured in this video is Darryn Capes-Davis who is a very prominent Bicycle North member.
Here is the map of the two rides and you can find them here on the Sydney Cycle trails Google Maps >>
Green is the Bella Vista to Schofields video path and Red is the route of the Smalls Creek and Windsor Rd Video
South Of Bella Vista
There are some nice shared paths south of Bella Vista. Here is a sample