You weren't very specific at all and as such I can only give you a couple of choices which have better search functionality and also some bells and whistles
1 )
) Auction Master on Curse.com is a good one. THe author reads all the comments and interacts with the community a lot. He takes bugs/ problems / feature requests very seriously and this is an amazing starter AH addon.
To watch some of it's advantages over the default AH UI , watch
THIS video. Between 0-4:10 he shows Auction Master and how you search buy sell with it .
2 )
Auctionator is another good one that is a little more known about. It was recently updated on curse and is what I personally use
To watch an intro to the addon, watch
THIS video, which shows how to use it as it can be a little iffy the first time you use it. He also shows it's settings and configuration
Hope that helped !