I think there are arguments for all of the photo-sharing sites, but I purchased a Flickr Pro account justa few months ago and think it's worth every penny. While Photobucket, SmugMug and Picasa Web Albums (from Google) are all good sites, in my experience I've found the community to be strongest on Flickr.

There's a good breakdown of photo-sharing sites on Lifehacker if you haven't already checked it out. It's here -- http://lifehacker.com/395900/five-best-photo-sharing-web-sites