A lot of us use flickr to store our photos online. Bought by yahoo in 2004, this service is the "gold standard" in online photo management, and is in some ways the poster child of web 2.0. Undoutably, Yahoo will eventually release a native flickr app, but for the time being we have Exposure, a free ad-suported flickr client.
Like other apps that take advantage of the flickr API, exposure first asks you to give Flickr permission to access your account. This is a tricky step, and one where the competing app klick fails miserably. However, I was able to sail through this process on exposure, giving me full access to my flickr library on my iphone. There are a number of different ways you can browse your photos, using flickrs "sets" (what most programs call albums), sequentially, or via search. You can also access all public flickr pics, and even see those pics near you, by tapping into the GPS.
The ads in the app are slightly annoying, the idea being to upgrade you to the full add free version. I am not sure I would spring $9.99 for that; nevertheless this is a solid product until the flickr app comes along and is the perfect companion to Shozu, which will easily upload your pics into flickr. (although again, one wants a single flickr app to do both, or, alternatively a way to see your mobileme pics from the iphone).