I use Flickr, which works OK. There are one or two steps more than I would like to get the URL for posting on the forum......but all the pictures load and stay where they're put.
I swear by http://www.getdropbox.com/. Dead simple to use (drag and drop to a window that is just like any other Windows window. Right-click > Dropbox > Copy Public Link.
flickr here... also for being able to edit the image easily once you've uploaded it...
picasa... cos any pic i take on my phone (G1) i can upload directly to this account... and then text people a link. cheaper than sending an mms as i have unlimited data and texts...