I know this has been done to death, and will probably open up a whole can of worms, but here it is anyway - having watched many unhappy tourists (US, British, Italian, German...) this weekend in a few different cafes, I think it bears repeating. The quality of coffee in the average Parisian cafe is not what one hopes for. Ordering - and getting - something close to what you would like can help make things more bearable. There are better coffee places opening up, and you can make decent coffee at home, but if you go out, here's what to expect in the average cafe:
Cappuccino should be drunk in Italy, period. In Paris, what you almost always get is an impressive souffle of froth and some useless brown water. Sometimes there's more brown stuff sprinkled on top. Costs a lot, looks impressive, absolutely no flavor. Definitely worth a trip to Italy.
"Cafe au lait" is what you drink at home, in your pyjamas, usually out of a bowl that you have had since childhood. When you want coffee with milk in a cafe, order "un cafe creme" or "un grand creme" - for a large cup of coffee with about an equal amount of milk, or "un noisette" for a small espresso with a drop of milk in it. I find "cafe creme" way too heavy on the milk, so I order "un double noisette" - a double espresso with a little pitcher of hot milk alongside.
Iced coffee is not always available, but when it is, it's listed as "un cafe frappe" (frah-PAY) - a tall glass of strong black coffee shaken with some ice and usually a lot of sugar, sometimes served over ice, sometimes not. You can ask to have it made without sugar, "sans sucre", and I'm sure you could ask for milk to be added, though I have never done this - "avec un peu de lait". I have seen "cafe glace" (glah-SAY) in a few places, and would expect it to be the same thing.
Cafe Liegeois (lee-ehj-WAH) can be very good, but more often than not it seems to fall in the same category as Cappuccino. Lots of show, pricey, but not a great beverage. If you want to try it, it's a little bit of coffee, chocolate ice cream, chocolate sauce, and a ridiculous amount of sweetened whipped cream, usually with brown stuff or chocolate curls scattered over the top. Sort of like an ice cream sundae gone astray.
I've left out two others, since I never order them: "cafe allonge" (ah-lawn-ZHAY) - espresso with an equal amount of hot water added, and "cafe americain" - which I think is the same, only with more water. I don't order these, since I believe some things are worth prolonging, but the taste of cafe coffee is not one of them!
Hopes this helps some folks...