I'm trying to figure mine out. I used a service called wImg, but then it disappeared. Then mirrorimg. Now it is gone. Now I use Imgur, but I don't know how long it will last. I hate Imageshack and Photobucket, so I won't use them.
I know the owners of blog wImg and Mirrorimg, Mirrorimg.net closed because the owner who was a friend of mine was having to pay heaps for the server as it was using 2TB of bandwidth which is heaps to pay for.
Imageshack and Photobucket are the most reliable IMO, they're two of the ones that have been around forever... I've seen many sites get down but those two stand strong :/
I use Vked and Minus alot, Minus is awesome. I'm an image hoster slut, I check out everything lol....
There is also...
Flickr
Image Coast
Imgplace
RemTEK
TinyPic
Webshots
XS
Don't forget to use social networks like Twitter, Myspace, Orkut, Formspring, Chime In, Blogger, Facebook and Tumblr... which all let you upload images.
I use my own imagehost, but if I had to use one other than my own I'd go with tinypic. Only reason I didn't want to use free hosts anymore is they delete images :great:
