I'm a property manager and Google Maps is very handy! I used my computer to create a personal map with all my properties (120 of them) and then I can quickly pull up the whole list on my Droid.
Karl's Mortgage Calculator is the best financial calculator I've found, and it's free.
AndiCar is an excellent FREE tool for tracking business mileage. You can log in the start/stop odometer, use the GPS, or just enter the total miles driven. Then enter a date, time, and purpose for the trip (not necessary). All the data is stored and you can export it to CSV for importing into an excel spreadsheet at tax time.
Zillow is a great FREE program for looking up properties for rent. Start with a great map showing all available properties for sale. Click on one and you get a pop-up with image, price, and basic details. Open it and get a detailed look, along with scrolling images! I haven't yet found a property in my market that was on MLS but not on Zillow.
I'm still looking for a program to sync contacts between Outlook 2007 and Google. In fact I'd settle for any program that could sync contacts between my Droid and Outlook! I could export them as .csv, then import to excel, then copy to my Droid, but this is time consuming instead of auto-sync and I really don't want to scroll through 200+ contacts in an excel file. If anyone can find something for this, I would sure appreciate it!!!