I agree that Quickbooks Pro (QB) is the best program, you can use jobs or classes to organized expenses and income and then you just use the same account list for all records. I've customized my QB so it works for real estate income and expenses and for each property I manage. QB pro is worth every penny and I usually upgrade every 3 to 4 yrs to the next version. I am using QB pro 7 right now and I really like it, especially the dashboard which allows you to go into the part of the accounting system you want to work.
I've tried lots of different software packages and always came back to QuickBooks. It's the most flexible product out there - easy for agent work and also configurable for property management (even 100+ tenant clients).