My wife and I currently rent our townhouse outside of Washington, DC. We searched a bunch of different sites, but found that realtor websites (we used Realtor.com and longandfoster.com, just make sure to pick "Homes for Rent" when searching) and hotpads.com were the best ones. As for looking for a rental "home" for a vacation, my wife and I used vrbo.com and homeaway.com (both are owned by homeaway I believe) to book out week-long honeymoon. Was definitely a great experience and can recommend the site to others!