I use a photo hosting site at Village Photos. For $5 a month, I get:
* 800 images up to 3MB each
* 6000 MB monthly transfer (that would be 60000 100K image downloads)
* Online tools include captioning, URL protection, private/public galleries, resizing of images, jpg compression and image rotation
I have used this service for over 2 years, and as far as I know it has never been down. And even though I post images here, I have never used even half of my monthly transfer. There are cheaper plans there too....