TinyPic is free and with the Cropper tool, it is super duper easy to store screen snaps online. Alt-PrtScrn captures the screen or current window, saves the image on disk, and, with the SendToTinyPic plugin, uploads the image to TinyPic, and drops the URL of the uploaded image on your clipboard. What used to take me 102 keystrokes ... PrntScrn ...open paint.net...save... open browser...upload...copy...switch windows...paste......where was I?.. etc etc... is now 2 seconds and one key-combo.
It also logs the URLs in a file so you can recall them later.
The build as of today doesn't do all this, you need the patch #3239. Download the cropper.Plugins source and apply that patch, you will be good to go.
Cropper also has a SendToFlickr plugin, though I haven't tried it.