Random photo posting on Flickr
Here is something fun to do, which I just did. Resort your iPhoto (or digital photo software of choice), by something other than date. Perhaps simply reversing the order would be sufficient for you, for others you might have to play with the sorting a little to get what you want. Then, pick some random photos from what you see and post them.
The inspiration for this came from setting my screen saver, on my iMac, to show random photos every few seconds. With about 13,000 photos in iPhoto, this makes for a really nice mix.