Archer Maclean's Mercury was originally released back in 2005 for the PSP, but can now be purchased and downloaded for your PSP via the Playstation Store, for a modest £4.79.
The basic idea in Mercury is that you control the flow of a very realistically modelled blob of mercury over a series of 3d levels. The path of the blob is dictated by real world physics. You can tilt the level in any number of directions using the analogue stick, and this in turn sends the mercury blob moving. This works quite well as you have a lot of precise control over the path of your mercury blob using this tilt system. Holding down the left and right shoulder buttons zooms the view on the 3d world in or out. The camera can also be panned left, right, up and down using the four symbol buttons.