Agent Insider Tip: Craigslist is my favorite... it's just like looking for yard sales! It is immediate and current. Hopefully, the city you are looking in has a friendly policy to allow agents to post directionals, because then you will effortlessly be able to see others available in the area. As an agent, I have had a high number of people show up to my Open Houses with a Craigslist print-out, or mention they found me there. There are even days I decide to do an "impromtu" Open House just because the weather is good, and I can do work from my laptop on site.. so up it goes on Craigslist! Sure, I will advertise an Open House in other places, but I go to craigslist first - it's a no brainer. Good Luck House Hunting! (I do not work for craigslist.... craigslist works for me)

Further enforcing the previous points - there really is not one single reliable source. Not all open houses will be scheduled early enough to make the Times and not all agents know to input there open houses so they get swept for the internet.

All answers thus far have some great information - the only thing I'll add is this - if you can't find your answer on-line, either have your realtor - or find a realtor who lives, works, and knows the MV, Kent, & Renton area well to provide you with the data as it comes available. I dislike self-promotion, but do live in between all three (Maple Valley zipcode).

Your agent should be happy to get a list of opens in any area that you would be interested in. A professional agent would be searching on the Northwest Multiple Listing Service, which encompasses all of Washington. Don't hesitate to ask them for this information. Although some might not be advertised as they could be opened at the last minute, most agents will post this information. Also If you are working with an agent, let the agent at the open house know that. I keep a list of all opens in any area that I am doing an open house at, as well as various comparables in the area.
Some agents may do this? Good Luck with your search.

Your agent should be able to send you a link that will have all of the scheduled open houses attached to it.

To add to the answers below. Yes, if the agent puts the Open House in the MLS it will feed to the various sites, but not all and not all as quickly. Redfin seems to have the most accurate data. But there is a glitch in the download that makes even Redfin's Open House info not as accurate as getting it directly from the mls. The mls is working on that problem. Windermere's seems to take longer to pick up the Open House entry than it does if there is a new listing or price change. It must require a different type of "sweep" of the new info go gather the Open House Data than it does to pick up new listings.

Often agents decide to have an Open House at the last minute, based on their work schedule. So you will never have a complete list of all Open Houses. Best to pick the neighborhoods by the Redfin list, and still keep your eyes open for additional Open House signs.

Noting Open Houses on Public Sites is a new thing. Not all agents know that major sites will pick this info up from the mls if they post it there. Once the word gets out, hopefully more and more agents will utilize that feature.

Questions like yours are very helpful, as more agents will read this and now tht they can show their Open House on the internet for free, simply by noting that info in the mls.

Trulia will list Public Open Houses (narrow your search criteria then select the home and if the agent is planning on an open House, then it should show up). Also if you visit Windermere's site http://(www.Windermere.com), Open Houses are listed there as well. And, the old standby still works (Seattle Times Sunday paper). Best of luck!

-Daniel

I believe Red Fin's site and some others are now showing some open houses when they have been uploaded to the MLS. Not all open houses are uploaded though...it is probably just as easy for your realtor to do the search for you though like Robert said.

Also...go through Craigslist on the morning that you want to go to open houses...you can narrow by areas and see what comes up then!

Your agent can do a search for you and provide you with a list. I am not sure where to get one unless you have access to the MLS. It also makes sense to provide a little more information, age of home, how big and so on. It is a pretty easy search to generate.