Just because I'm always forgetting and looking it up over and over again. GTX, GTS, GT, GS, and G.
Going from left to right is the easy way to determine how good a card is compared to other cards in the same model number.
In other words a GTX 280 is suppose to be better (and pricier) than a GTS 280. This may not always be the case though but a good rule of thumb.