With the new Spectator Patch for League of Legends, spectating normal and ranked games is now possible. You can either watch a game your friends are in or there are also 5 "featured" games going on at the home screen. Are these just random ranked games? Those at the top of the ladder? If the former, is there a way to watch the high level "masters" games?
From the Darius patch notes:
Spectator Mode tends to pick skilled and slightly-above-average players. After this patch, it will choose exceptional players more often. Normal, Ranked, and even Bot games can be featured, though.
From personal experience, it seems like the five featured games are arranged according to Elo. From left to right, the best players will generally be in the first game, and gradually decrease in skill as you scroll to the last featured game.