Reducing document figures size

[Rich Shepard]

I have a 37-page report and the pdf size is 7.3M because it includes 34
figures. Some of these figures are digital photographs (720x480dpi, .png),
some are spatial maps produced by GRASS (.pdf), and some are lattice plots
produced by R (large amounts of data display slowly, .pdf).

Is there a format that would preserve image quality but consume less space?
I'm sure that ImageMagick's 'convert' will do the job. I've tried converting
PDF files to EPS but the quality is noticeably degraded.

Ideas most welcome.

Regards,

Rich