Here are a few sites I’ve found useful through the years:
Ian McIntosh
Ian is the keyboardist for Jesus Culture and has recorded on over 50 albums. He has a lot of great tutorials when it comes to keyboards and sound design.
Multitracks
Multitracks.com hosts studio tracks from popular worship albums including albums from artists like Hillsong, Jesus Culture and much more. These backing tracks can be a great way to easily add to your Sunday morning sound.
Brian Nagel
Although not recently updated, Brian has a couple of great MainStage tutorials and a few handy downloads for you power users.
Abel Mendoza Productions / Synthsation
These Synthsation sound packs are a great way to kick-start your synth patch library. There are 7 currently available for $30 each including pads, leads, pianos and much more. Especially if you’re not a sound designer, $30 is a great deal!