When I started with click tracks and loops many years ago I began with a super simple (and primitive) setup. I’d create a drum loop in my software (Stylus), burn a CD and play it from a portable CD player on my keyboard. The drum loop would be fed mainly to the drummer through monitors so he could keep with it as we had no budget for in-ears. The soundman would mix the loop into the live sound.
Next I graduated to using a laptop at my keyboard but still we used regular monitors. This was in a church of about 300.
As I’ve played in mega churches I’ve seen the other side of things – using in-ear monitoring systems. The church typically purchases glorified ear buds that fit securely in your ear – you don’t hear anything but the mix, no outside noise. These ear buds are far more advanced and expensive than what you get with your iPod and can cost hundreds of dollars depending on fidelity. I see lots of Westones in these churches.
LoopsInWorship.com has a good rundown on what equipment to use – take a look at their tutorial. The main contenders are Aviom and Hear Backs. I have a friend who plays at a smaller church who bought the Hear Backs since they’re less expensive and he hates them. He says they’re always running out of channels.