Ray Ban's iconic Wayfarer model might be my all time favorite due to their obvious embodiment of everything classic, badass and down right awesome. With that being said I think that people often jump into buying a pair without giving any consideration to the various models that Ray Ban has to offer. It's always better to try sunglasses on in person so that you know without a doubt they look good, but at the same time it's also integral to get a handle on the situation ahead of time to prepare yourself for the purchase. Keep in mind that there are a few other models in the Wayfarer family not talked abut here (the folding RB4105, the hipster RB2143, etc.), but I am overlooking those because you shouldn't be buying those in the first place.
The Original Wayfarer - RB2140
The New Wayfarer - RB2132
The New Wayfarer was introduced a few years back as a smaller alternative to the original. While they definitely are smaller I actually think Ray Ban messed with the proportions a little too much and the glasses seem more "squished" that anything else. Granted this shape is much more appealing to people who think the original is a little too big or intense, but keep in mind that it does lack some of the edge and angles that made the original so iconic.
This now defunct model, being phased out by Ray Ban, is the holy grail of Wayfarers as far as I am concerned. It really is the perfect combination of the two styles above, keeping the personality of the original while streamlining the shape just enough with its trimmed up frames (especially around the lenses) as seen on the New Wayfarer. While it's hard to tell the difference between this and the original on a computer screen, in person you can really see the improvements - I am assuming these minute differences are what caused Ray Ban to discontinue them in the first place as it must have proved confusing to customers. Keep in mind that you can still buy the RB2113 all over the interwebs and many stores still have them in stock.
In closing, make sure you know what you are getting into before you drop upwards of $100 on a new pair and try them on in person if you can. If you ever want to see the model number of the pair you are trying on it is always listed on the inside of the left stem and be sure not to overlook the importance of lens size either, even on the same model, as I have often found that is the most important factor. Oh yeah and before I forget, only black and tortoise shell please - unless of course your style icon is Lindsay Lohan.
[Editor's Note: The RB5121 is an optical version (for prescription glasses) of the RB2140.]