XLS - basically the 4 door sport version. As close to base model as you can get.
XLT - basically a step up. You added body colored molding (most tf the time), a nicer interior overall. With XLT you can add a lot of things, like Leather, CD Changer, Sunroof, Etc etc...
Eddie Bauer - the nicest 'non grandpa' looking lol. You add leather (almost always), a nicer stereo, the seats have the EB logo stitched in them, and you get two tone paint (usually tan on bottom).
Limited - top of the line (cept for customs and Anniversary Editions) Includes leather, computer console (temp/engine check/milage info/travel info), roof rack of course, nicer wheels, nicer "stuff" basically.
There is more info available on this. Also, some of this differs, depending on year of make. What year/years are you looking at? Try using the "search feature" located at the top of this message board, and search for "Trim Levels, XLT, XLS" that should give you some hits...
Welcome to the board!
--Bryan