Here is a standardized list for imagery that the Wherigo Media Group follows as much as possible.
For both the PPC and the Garmin device, we hold to a 230 pixel width. However, we use different lengths to make the most out of the use of the media while playing nice with possible words and hopefully your eyes.
MEDIA SIZES:
(height focused)
[Width is always 230 pixels]
GARMIN:
Zones : (all 1 size) NAME: zone(zone name)_garmin.jpg
W/ Text : 180 (preferable, meaning we mostly use this size, regardless of text)
or W/out Text : 230
Object details : 250 NAME: (media object)_garmin.jpg
Messageboxes : 230 NAME: (media object)msg_garmin.jpg
Tasks : 230 NAME: task(task name)_garmin.jpg
PPC:
Zones : (all 1 size) NAME: zone(zone name)_ppc.jpg
W/ Text : 130
or W/out Text : 174 (pref)
Object details : 174 NAME: (media object) _ppc.jpg
Messageboxes : 130 NAME: (media object)msg_ppc.jpg
Tasks : 130 NAME: task(task name)_ppc.jpg
Icons : 32x32 NAME: icon(media object).jpg
Posters for Web : 120x150
Cartridge Detail Image : 230x130 (this is the image used on the detail screen in when you click on a cartridge from your list)
SAVING DETAILS:
Save for Web
High, Optimized JPG
70 quality
I hope this helps. We're still developing an audio standard. Feel free to let us know what you come up with.