Everpix is mentioned in another comment. I tried Everpix last year, and it looks like since then they've made it possible to basically store photos in the cloud (without keeping a local copy). Could be an option...
Don't want to keep banging on about it, but yeah Everpix is the solution. Install it on the desktop and Sync the iPhoto library. Install the Everpix app on the iPad, £3 a month, job done.
Last time I checked though Everpix doesn't do video. I have all sorts of little video clips and I desperately wish Everpix would handle them as well as my photos, I don't want to have to split them up or deal with them differently.
From their website, I see no mention of how much quota or space you get to store photos with them. Am I correct to assume that you have infinite space?
Yes
Wow, yeah, it looks like Everpix is exactly what he asked for, and more, including multi-platform support (not just iOS), and for exactly the price he specs -- $5/month.
He also said unlimited video.
Yes, I use Everpix and I've been really happy with it. However, I like the photo upload tools that come with Dropbox, so now I collect, sort, and edit photos in Dropbox, then I transfer them to a static(ish) Everpix library that distributes them back to my iPhone/iPad/browser. Seems kind of circular, but it works really well. And I have 170,000 photos in the cloud for less than the cost of a Dropbox upgrade.
Everpix doesn't support Android just yet I believe - someone correct me if i'm wrong!