www.magicbullets.com/forum/ (my attempt to bring us all together) Dan
www.mrlandlord.com (property management) Jeffrey
www.thelpa.com/lpa/index.html (landlord protection) John
www.zipreports.com (credit checks)
www.tenantcredit.com (credit checks)
www.infocredit.com/ (background checks)
www.pretrieve.com (try it you’ll like it!)
www.creditretriever.com (credit reports on tenants)
www.skiptracers.com (find the tenant who owes back rent)
www.landlordlocks.com (one key for all the rentals)
www.rentracker.com (software)
www.rent-right.com (software)
www.rentalsoftware.com (software)
www.landlordsoftware.com (software)
www.thetooldirectory.com/main.asp (tool directory)
www.thelpa.com/lpa/free-forms.html?id=nyy2upaZ (free landlord forms)
www.screeningservices.com/forms/grab-bag.shtml (free landlord forms)
www.homefindersbulletin.com/docs/checklist.pdf (free tenant move-in checklist)
www.naahq.org/resources/econ.aspx (apartment owner’s industry news)
www.housingfinance.com/aft/ (Apartment Finance Today)
www.reiclub.com/real-estate-business-tools.php (R.E. tools for investors)

I have used many of these myself. In particular I want to throw in another recommendation for landlordlocks.com. We are in the process of converting all our rentals to these locks. The concept (one master key, ease of changing tenant locks) is fantastic, and the company's customer service is second to none.

Use them, you won't be sorry.