Currency and MC also make excellent trade bait. I've managed to lead in tech early (up to emperor) by going from monarchy to a currency beeline, then popping a GM from the glh for MC. Trading either of those two techs around, it's not hard to end up with everything anyone is willing to trade. In any start with more than two opponents on a continent, someone will tech alpha fairly early and trade it off for a roughly equal value tech if you have a monopoly on the trade bait.
It's funny...whenever I have a monopoly on alpha, I hold on to it like a drunk with a bottle. Being the only one who can trade is a huge advantage, but one AIs seem to vastly undervalue. While currency, CoL, Aesthetics and MC are all key gateways to lines of research, wonders and new tactics, none is a gateway the way alpha is. This has created a strange tendency...because I value alpha so much more than the AIs, I almost never research it myself.
The other tech that AIs seem to undervalue the power of a monopoly with is Scientific Method (oil location, prereq for 2 GP granting techs). But that's starting to ramble off topic, so I'll shut up now.