I have had trouble getting the money together to buy a digitizing tablet, and it would cheer me up to know what kind of digitizing tablet the artists were using to create classic games like Super Mario World and Sonic The Hedgehog. Part of me feels that maybe there is a way to make games without 2000+ pressure sensitivity levels. Does anyone know which models were widely used by console developers at the height of 2d gaming, and what their specs were?
I doubt they did. The majority of the true old school art (80's to early 90's) was done with a plain old mouse and pixel-pushing (raster) software like Deluxe Paint (now known as Cosmigo Pro-Motion).
As for when tablets did become really widespread and usable in the sense you know them today (perhaps mid 90's onward), Wacom was pretty much a big name throughout.
You can be sure that even the lowest end of what you buy new today will be better (and better supported in terms of drivers) than what they used back then. If I were to buy a new tablet now, I wouldn't go for anything too fancy, I reckon a Wacom Intuos 4 would be fine, IIRC there's a b5 size one that has what most artists need.
In addition to Nick, Wacom is the only brand that can be suggested with eyes closed & they have low price models.
I own 2 Wacom tablets, one I bought 3-4 or more years ago. The point is it still acts like brand new. Unless you break the pen (which can be bought separately), the touch surface shows no sign of age.
A few months back I bought another Wacom Bamboo. I suggest you to go for this one, as it's not expensive. I have heard a lot of high profile artist that still use their old Wacom tablet, cause it still works so well and they don't want to shift to something else for no reason.
Intuos are high-end artist models. See the feature list. If you don't need any of these, then simply go for the Bamboo series. It wont disappoint you. Paying a little more now will come back to you as a rare service in the long run.