The National Association of Certified Home Inspectors (NACHI)
is the world's largest, most elite non-profit inspection association.
http://www.nachi.org/index.htm

St. Louis Landlord site
http://www.stlouislandlord.com

CRE Online Clubs - Real Estate
http://www.creonline.com/real-estate-clubs/index.html

Bigger Pockets Forums
http://forums.biggerpockets.com/

Zabba - Free Search
Find everything available on the web about yourself or someone else!

Mr. Landlord Credit reports (fee based)
http://www.mrlandlord.com/html/creditfaq.html

General Reference

Find that Property!
http://maps.google.com/

How-To's

Home Improvement How-To's
DoItYourself.com

Home Improvement How-To's
http://homestore.com

Get rid of tough odors with OdorXit®
http://www.odorxit.com/

MISC.

The Landlord's Guide to QuickBooks, is a CD course designed especially for Landlords and Property Managers to help them learn QuickBooks. It is simple to use and simple to understand because Nancy Neville uses visuals and step by step instructions on how to fill in the blanks and why. Not only has she made learning QuickBooks easy, but to help you even further, she has incorporated her own Chart of Accounts and Item's List into the program for FREE
http://www.sunriseinvestments.net

HTC Apartment Manager V2.1. This property management software package is intended for the small to medium sized owner or manager of several to numerous rental properties.
http://www.aptmgr.com

Great FREE information (mortgage templates, RE Investment templates, profit and loss templates, etc.) from Stephen Nelson, author of Quicken for Dummies and QuickBooks for Dummies.
http://www.stephenlnelson.com/free_stuff.htm