Hardly an exhaustive list, this is as much a tool for me to keep track of sites I use,  as it is a forum to share my "bookmarked" sites with others.  There's SO much great stuff out there, I often find the task of sifting through it all daunting.  So, I've created my own annotated list, which I'll keep adding to.  Here's my slow start, arranged in no logical or useful fashion. :)

(By the way, if I've listed your website below and I didn't credit it properly or you want me to "unlink" it, just say the word. I don't mean to step on toes, and this is obviously for educational purposes only.)

Kathy Shrock's Website - Kathy is a guru when it comes to educational technology.  Her site has links to a treasure trove of resources about technology and teaching.  (http://kathyschrock.net/)

Math Live - This is a wonderful set of animated math tutorials on the 3-5 level. (http://www.learnalberta.ca/content/me5l/html/Math5.html)

TV411 - More online tutorials, this time in a wide range of areas. These are intended for adult remediation, so they aren't particularly flashy or kid-friendly. Nonetheless, they cover a lot of useful content that is relevant for upper elementary students. I particularly like the vocabulary section.
(http://www.tv411.org/)

Poetry Frames and Forms Website - This has a list of SO many poetry formats that I've never even heard of.  In general, I try to teach poetry WITHOUT using prefab frames or formats, but it's still a useful scaffold from time to time.  The website isn't elegant, but it gets the job done.
(http://ettcweb.lr.k12.nj.us/forms/newpoem.htm)