This is a good question! I too would like to know what the players like SteveO, Gus (is he still around?!?), RealOG, LagunaLauren, JScott (and others, sorry if I haven't named you) are using for their properties. With a quick search into google, I see companies that provide software for listings, some for investment analysis, and others.
"For Real Estate management software", I have run across with a quick search:
Property, Asset and Investment Management Software l Yardi Systems
EASIEST Property Management Software: LandlordMax
Property Management Software | AppFolio.com
Property Management Software | Buildium
Residential Property Management Software | Intuit Real Estate
(I endorse NONE of these companies)
It'd be interesting to hear what others use, but I'm sure there are differences in what your needs are. For example, did you want a desktop application or one available through the web? What exactly do you need to track? Is it day to day management? If so, how many units do you need to cover? Etc. If you can give a more detailed picture of your needs, and what your budget may be, the advice you'll receive will no doubt be more beneficial.