This may not be exactly the type of thing you are looking for, but honestly I have gotten quite a few ideas from perusing the TED talks, some of them about education, some about more specific subjects, but they lend a great deal of insight and challenge the way I approach planning and teaching in a way that has been really helpful. You can find them on ted.com or if you know who or what topic you are looking for most of them are on youtube.com as well.
You are already on the web site that provides excellent lesson plan ideas. The materials from Prestwick House are wonderful. There are also documents, many of which are free, that teachers have uploaded on a variety of subjects. These include lesson plans and activities. If you teach literature, the study guides on enotes can serve as a basis for your lessons.
I have found many helpful lesson and unit plans on enotes. Often Prestwick House unit plans are available through enotes, and they are especially well written.
I also use webenglishteacher.com and sometimes awaytoteach.net which offers interesting activity ideas and higher-thinking analytical plans.
What subject do you teach? If you are an English teacher like me, or if you teach English at all, Web English Teacher and Read Write Think are both extremely useful resources. I've found tons of useful activities on these two sites. I do generally have to modify the plans a bit for my classroom and what I need to teach specifically.
Seeing that the question is about the very nature of finding lesson plans online, I would consider using the enotes lesson plan section of the site. I think that there might be a challenge in using any online source for a lesson plan because it might fail to take into account the specifics of your classroom. Hence, some modification will be almost inevitable. Yet, I would feel fairly comfortable with the lesson plans on enotes for they have been submitted by real teachers who have experience in the classroom. I know from personal experience that the lesson plans I have submitted have been tried (by me) and have been field tested with relative levels of success. Lesson plans at enotes can have the added benefit of being created by either educational companies or by the teachers themselves, which will allow you a great sampling of how to approach a lesson. I think that examining what is there on enotes in terms of lesson plans might be a good start for what you plan on teaching and exploring in the classroom setting.