Random thought: Google, Microsoft and Apple are all monopolies in their own rights.
Google, the fast-becoming monopoly of the internet. They dominate over internet searches, ads, gmail, gears (online apps), and soon over desktop search too, now that Microsoft has caved in to Google's harsh request to make Vista's Instant Search accept third party search software. With Vista now, if you install Google Desktop Search, this will run together with Instant Search, meaning decreased system performance as two indexers are running simultaneously.
Microsoft - need I say more? The market share of Windows says it all. Complete monopoly. That's why the EU is always after them, and they are almost always entangled with anti-trust lawsuits.
Apple, the lethal combination of iTunes and iPod has locked away any other form of competition in the music player market. If not for iTunes on Windows, the iPod wouldn't have made it big. In the music player market now (US), iPod ranks first, then the Zune, then all other music players by other companies.
Monopoly, its more than a game. It's being infused into our everyday culture.