Ancestry.com has the largest collection of online death records, but you would have to have a subscription to research there. FamilySearch Labs has a collection of free death records for some States, for which you can check out which ones here:

http://www.familysearchlabs.org/
click onto RECORDS SEARCH, then click onto the map and a list of searchable databases comes up.

Various states have death records online, but most are by County, you would have to click onto each individual State database that has death records to see what's there.
You are not going to have much success at finding death records unless you have some idea of where you want to search, then you would need to look at the records available for those areas.

Deloris