Simon Moss reminds me that there are precursors in many other first-order transitions too.
Some of these transitions are very much like the freezing of water. There are some precursors in the water-to-ice transition: for example, below 4 C water starts becoming less dense as the local atomic arrangements become more open and ice-like. In order-disorder transitions in metallic alloys, there can be precursors which look much like the fluctuations near second-order transitions but which are cut off by the transition before they become really big.
In other systems, the precursors may be more like our tweed: driven by disorder, with long-range effects due to elastic strains and stuff. For example, there are systems which change volume and/or crystal structure without an overall change in shape.
James P. Sethna, email@example.com
Statistical Mechanics: Entropy, Order Parameters, and Complexity, now available at Oxford University Press (USA, Europe).