It would be handy to have 1000/500 hPa thickness overlaid on the mslp chart.  To get 1000/500 hPa thickness you only need mslp and 500 hPa geopotential height.  Thickness can then be fairly well approximated using, for example, an isothermal calculation of 1000 hPa geopotential from the mslp.  I've done this in GRADS and found the output agrees very well with 'real' ncep thickness.  (From the 500 hPa height, you can also calculate wind and vorticity, albeit only geostrophic, but at least you get a feeling for vorticity advection.)  I find frontal analysis much easier with a thickness field.

Somebody suggested sig wave heights, which I can only say is a great idea.

I emailed the suggestion in, but I guess the programmers are a bit busy to read everything in the in tray!

Also, perhaps it might be possible to put surface wind divergence/vorticity in?  Not really as useful as precip, of course, but given that the user has already downloaded surface winds...