Flickr. Use it to post photos online to share with just your friends (private) or the whole world (public)! You decide. Signing up is a simple process. Since I already had a Yahoo! Mail account, I was able to use the same username and password.
Once on Flickr, your pictures can posted directly to your blog. (I'm typing this in Flickr right now.) You can add comments and tags to your pictures to make them searchable. I've got numerous pics from my fishing trips in the Eastern Sierras. To find them, just search for all the pictures with the tag "Sierras". Want to see all my Flickr photos? Just click on photo on this blog. Once there, click on "dgrice's photostream" to see my other photos. If you want, feel free to add comments to the photos and even subscribe to my photostream (using RSS).
What can teachers do with this? If you have photos from your vacation that you want to share with your class you can post them on Flickr and give students a link to access them online. They can use your photos in their multimedia projects or use them as writing prompts.
You can also use your vacation photos as a geography lesson. The map feature in Flickr lets you plot your photo locations. To see where my picture was taken, click on it and look under "Additional Information" to see where it was taken. Click the (map) link. For fun, have your student try to guess where a picture was taken, or create a Flickr for your class and have them bring in their own vacation pictures, upload them (with parent permission, of course) and then plot on the map where their pictures were taken.
A word of warning: I suggest you give students a direct link to your photos rather then having them go to Flickr and search everything. Since anyone can post photos to Flickr, some of the images may not be appropriate for use in the classroom.