An auction game that I picked up in a math trade recently (and then donated to my FLGS after it got quite wet in the tornado) was Ra.
In Ra, players are attempting to purchase different tiles to ensure that they either score victory points (or don't lose victory points) at the end of each epoch (scoring phase). To do this, each player starts with three bid tokens of different numbers. On a player's turn, he gets to choose between 1) drawing a new tile from the bag and adding it to the set of tiles available for auction (this could potentially start an auction), 2) purposely start an auction, or 3) steal one of the tiles that is currently in the auction pile (this can only be done if they have a special "god" tile that they have previously purchased). Whenever an auction begins, the players each have one opportunity to place their bid using one of the bid tokens that they have available. The winning bidder gets all of the tiles that were on the board, in addition to the bid token that was in the center of the board (which they turn facedown until the end of the epoch), and then they place their bid tile in the middle of the board. Play continues this way until all of the players have run out of face up bid tokens, or until a certain number of "Ra" tokens have been drawn (Ra tokens are tokens that instantly start an auction when they are drawn from the bag). One of these conditions signifies the end of an epoch. At this point, players score based on the number and selection of tiles they own. Rinse, repeat. (At the end of the third epoch, a few extra things score). After three epochs, the person with the most victory points wins!
The first pro for Ra is how the bid tokens work. I absolutely love this mechanic - and it really gives the game a different flavor than any other auction game that I have played. I love so much about them, that I'll probably have to split this into several "pro's". The first bid token pro is that they switch out whenever you win an auction. Because of this, the person with the highest token at the start of the game won't necessarily have the ultimate trump throughout the game. In fact, depending on what he purchases, he has a chance of trading in his high token for the #1 (worst) token, in which he'll only be able to win an auction if nobody else bids! This causes there to be a sub-game inside of Ra - each player being careful to not only collect the best tiles, but to also make sure that they don't wind up with the worst bid tokens. But even then, a skilled player can do well with very low bid tokens if he adjusts his strategy; he must simply start auctions more often so that the players with the better tokens don't get the luxury of spending them on a large set of tiles! The bid tokens are just plain awesome.
The next thing that I like about the bid tokens is that when you win an auction, you have one less token available to bid with for that epoch. Therefore, nobody can ever win more than three auctions in an epoch. This really helps keep any single player from gaining too much of an upper hand in the game. It does, however, allow an opportune player to have the privilege of having a "push your luck" element at the end of an epoch. If one player can outlast everyone else to where they have used all of their bid tokens (thus he is the only player still playing), he can keep drawing new tiles from the bag - but if he fills up the Ra track, then he will lose all of the tiles that have been drawn, as there is not an auction once the last Ra is drawn! The bid tokens continue to be awesome.
The last pro that I will mention about Ra is that there are both positive and negative tiles that can be drawn. Some of the tiles are "destruction" tiles, and whoever wins the auction that contains these tiles loses two of his useful tiles of the given type (for example, gaining a "Pharaoh" destruction tile makes you discard two of your "Pharaoh" tiles). This prevents the push your luck element that I previously mentioned from becoming overpowered. It can also drastically change the mood of a set of tiles instantly. A set of tiles that would easily draw out the largest bid token can go from being completely wonderful to only being somewhat good in a single draw. This is a nice element to the game; whereas the game would probably still play well without it, this element really adds a nice touch that helps take Ra to the next tier of games.
The only real con that I found when playing Ra is that passing the bag around for everyone to draw a tile on their turn winds up taking about as much time as the actual gameplay. After the first time playing, we quickly gave that up and designated a single person to draw for everyone. This speeds up the game as you're not constantly worried about passing the bag, making sure that the tiles don't fall out, and making sure you don't accidentally cheat while drawing.
Overall, I give Ra a 9.5/10. In my opinion, this may be the best auction game on the market. It is quick and easy to play, but also has the depth to keep me wanting to play it again and again. I would highly recommend that anybody that doesn't have a strong aversion to auction games make a point of trying it out.
If you like auction games like Ra, you might also want to check out Princes of Florence, Power Grid, and Furstenfeld. And, for another opinion of Ra, you can check out this Review of Ra on I Slay the Dragon.