Is there a standard rule for how much wattage you need for a bathroom? I am re-doing my 6' x 8' bathroom with 7' ceilings. I have 1 60 watt light in the shower. I have no cans, etc. in the ceiling in the main sink/bathroom area. Are 3 60watt sconces enough light? We will have 2 mirrors (one over each sink) and a sconce on either side and one in the middle???

That sounds like probably enough for that size a room. But make sure that you have lights about equal distance on both sides of each mirror.

If you have sconces heat-safe for 60W bulbs, you could replace those with compact fluorescent lights that give 2-3 times as much light, without any heat problems. So you have the option of using brighter bulbs if needed, but CFL, not incandescent. (I would recommend that anyway.)

But really, since you're redoing the whole bathroom anyway, give yourself some options. It will cost almost nothing to build in some extras, in case you find out you DO need more light in the bathroom.

Put a ceiling box in the middle of the room, and run an electrical cable from it to the switch by the doorway. Just leave the cable unconnected, and cover the box with a blank face plate, painted to match the ceiling. You could also do this to the appropriate location for a fourth wall sconce, and to a spot above each mirror. Having the blank boxes there, and a cable into each of them will make it real easy if you ever decide to add more lights into this room. Or a ceiling fan. The cost is minor now, but makes future changes easy (and cheap).