Unfortunately there isn't such a list - at least not officially.
Exactly which cars are within a class will vary from company to company, from year to year, and to some extent even from location to location. The rental companies will give you a "sample" of the type of car you may get for a specific class, but it's extremely common (almost expected) to get something different to the specific model that they display on the basis of the "or similar" entry.
It's also possible that you'll get an "upgrade" from the type of vehicle you rented. When it comes to hotels, upgrades are a good thing. For rental cars they can be good or bad - especially if you get something with significantly lower fuel economy that what you reserved. In most cases if you get an unwanted upgrade you can ask them for a vehicle closer to what you reserved - presuming they have something available they will give it to you and give the upgrade to the next person.
There is one exception to this, which is that some companies will allow you to rent a specific type of vehicle. With Hertz you'll see that as a entry under/next to the model that says something like "Reserve this Exact Model" - if you select one of those vehicles you're going to get exactly what you picked. Normally these only apply to specific type of cars that are "special" in some form or other - sporty cars like the Ford Mustangs, or Hybrids like the Prius are two examples you'll frequently see listed like this. (Hertz even has a few Porsches out there now that fit into this category!)
Unofficially, there are groups of people who maintain "fleet lists" based on reports of what cars people received. For Hertz, there's such a list available on the Flyertalk Hertz forum. With a bit of searching you'll probably find these for other companies too (I only know the Hertz one as that's who I almost always rent with!)
As far as knowing whether you've got what you paid for, you can normally tell that (again, with Hertz) by looking on the keys. There will be be a one or two letter code on the keyring that specifies the category of car you've got - A for Economy, B for Compact, C for Mid-side, F for full size, or G for premium. Sometimes there will be a Y in front, which designates that it's a "fancy" version of that model - so a YC is a Mid-side, but in some way or other it's better than a normal Mid-side (maybe newer, lower miles, leather seats, etc). These codes are also listed on the page above against the type of vehicle.