Auctionator is one of my favourite addons for doing Auctions.
Why? Because listing up auctions has never been so easy!
My favourite aspect of auctions towards Auctionator is that you can easilly just place an item that you’re wanting to sell in the auction house, it will search for current price and undercut, and all you need to do is press post. Simple as that.
You can also see how much you have posted auctions in the past, which is a great feature, so you know if you’re posting it for more or cheaper than you have been.
Version 4.2 Link: http://wow.curse.com/downloads/wow-addons/details/auctionator.aspx
Version 3.3.5a Link: http://wow.curseforge.com/addons/auctionator/files/52-version-2-6-3/