Search for cameras by weight.

dpreview.com has added a camera feature search, so you can search their database for cameras
that have a specific feature. One 'feature' that you can search is camera weight.
go to:
http://www.dpreview.com/products/search/cameras
then click 'Show advanced search filters'
click on 'Weight' under Physical.
set the slider to the weight range you seek.
For example, there are 4 cameras in their database that weigh less than 100 grams:

http://www.dpreview.com/products/search/cameras#criterias=SpecsCoreParams%2CSpecsWeight%2CBrand&includeDiscontinued=No&sort=lowestPriceFirst&view=grid&page=1&paramSpecsCoreParamsBodyType=UltraCompact%2CCompact%2CSLRLike%2CLargeSensorCompact%2CRangefinder%2CMirrorless%2CCompactSLR%2CMidSizeSLR%2CLargeSLR&paramSpecsWeightMin=0&paramSpecsWeightMax=100&paramBrand=Kodak%2CNikon%2CSamsung

the lightest is the Samsung ST30 at 87 grams. If you click 'include discontinued',
you also get to see discontinued cameras in their database.
There is a 60 gram discontinued camera, but it's only 0.3 megapixels.