Found a really good coffee bar in North Sydney recently (thanks Chris!) and that prompted Chris and I to embark on a little experiment I've been meaning to do for awhile. I read somewhere about "cafe ristretto" which is supposed to be a short pull from the espresso machine, but in actual fact usually just gets you funny looks before your espresso in most cafes. Then a new cafe opened downstairs in my building that has on its price list "espresso", "doppio" and doubles of either. So having discovered this other coffee bar where the barista actually seemed to have a clue, we each ordered one of each (espresso, doppio, and ristretto) and then chatted with the dude while we tasted them next to each other.
Espresso is the stuff you're used to: you put a single shot of the good stuff, finely ground and well-tamped, into the single-pour fitting of the machine (with 9 bar of pressure and at 88C - I'm not making this up, and it is actually important!) and pour for 22 seconds. It is yummy, but slightly bitter.
Doppio is supposedly just another word for a double espresso: you use a double dose of coffee and the double-pour fitting - just like you were making two espressos at once - and run them into the same cup. Ideally, this should really be the same stuff but twice as much. Tasting mostly bore this out, though I think the crema comes out different when you pour them both at once. (This doesn't seem to match what the cafe downstairs does, which _may_ explain why they have doppio and double espresso on the menu. Or it may just mean they have no idea. I've never ordered a double doppio, so your guess is as good as mine.)
Ristretto is a single shot of coffee, in the single-pour fitting, but poured for half as long (so its very small.) Literally "restrained" in Italian. Supposedly this gets more of the flavourful oils that come out early in the pour and less of the bitter flavours - including the caffeine - that come out later. I can't speak for how much caffeine it has, but its definitely a richer, sweeter flavour; very nice.
Some other, less interesting, ways of making your coffee bigger:
Cafe Americano: An espresso with hot water poured in it (Bah! Stupid Americans!)
Espresso Lungo: An espresso poured for longer; supposedly somewhat bitter.
Mega-mug of Turkish coffee: don't go here unless you're
(Oh, and I've just had four shots of espresso with lunch; I can see through time.)