I use Picasaweb for mine. Since I have had the account for several years I am "grandfathered" and get 20 GB extra space for $5 a year. But it looks like if you are new you have to pay $2.50 a month for 25 GB of space and you have to use Google+ instead of Picasaweb. I HATED Google+ when it first came out and hijacked my Picasaweb. Had to ditch Google+ altogether in order to get Picasaweb back. Not sure if it is any better now, but I doubt it.
Shutterfly is pretty easy to use. Free, unlimited storage. (I believe)