This is one of the coolest things I've ever seen in a gardening catalogue. The Irrigatia really impresses me and I quite want one for when I get my allotment, which in theory is imment. Compared to last week's and a fortnight ago's devices, this one seems like it actually really worth getting, especially if you live in a dry area. It's basically a little box of solar cells which is connected to a pump. You just pop it into your water butt or tank, and install the solar box on the wall. The manufacturer states that it will water every three hours, or as necessary. So, if it's really sunny, it'll water more often.
It comes with several drippers than can be spread out across your garden or allotment, and there is also a model that gives you longer pipes and even more drippers, if you've got a large area to look after.
It's under £100, looks like it's pretty easy to install, and is free to run thanks to the solar power! What more could you ask for?