This is for some popular drinks, at 20 oz (that's venti to you Starbucks addicts. You know who you are...)
Numbers based on the first site I mentioned earlier.

Coke: 57 mg
Diet Coke: 76 mg
Pepsi: 62.5 mg
Diet Pepsi: 60 mg
Dr. Pepper: 68 mg
Mountain Dew: 92 mg

American brewed tea: 100 mg
Import brewed tea: 150 mg
Drip coffee: 288 to 438 mg (Starbucks is 415 mg, but see below)
Espresso: 1000 mg (but who drinks 20 oz of espresso, anyway?)

So what's the ratio? So Coke:tea:coffee really is about 1:2:4, but there is a lot of variability in the coffee levels based on fineness of grind, method of brewing, etc. Somewhere on that second website, it says: "A recent laboratory test sampled a series of Starbucks Breakfast Blend brewed coffees. The caffeine dose varied from 299.5mg right up to a massive 564.4mg per 16oz cup! What’s astonishing is that the 6 samples were obtained from the same outlet on 6 consecutive days."

So 1:2:4 is a good rule of thumb. And we all know Mountain Dew is high for soda, now we know that it's about as caffeinated as tea!

(and two liters of Mountain Dew has less caff than a 16oz Starbucks drip)