If you want or need a really high data rate system then there's probably no alternative to cable, but that might mean drilling holes in walls etc. For lower data rates some of the mains distribution systems are quite good - usually HomePlug at 85 Mbps or the AV versions as 200 Mbps. They are pretty much plug and play, though if you want to play around with configuration you can. You'll still probably need a short ethernet cable at each to link your kit in.
I have several Zyxel units connected together, and they've been working for a few years now. I hear that some others also work OK, though there may be some to avoid. Actually I connected two routers together as they were on a cheap offer. This works but configuration is slightly tricky initially, as you have to fool one of the routers that the other one isn't there so you can set the parameters, but it can be done, even though the suppliers don't recommend it particularly. One router has to be set up as a bridge. Some routers complain a bit if they're not connected to a DSL line. Once I got it working I linked in another router with an additional Zyxel extension plug.
Might be worth checking out, though cable is cheaper if you don't mind doing the wiring.