Is there a searchable list of applications that support OS X's resume/autosave/iCloud features?
I don't believe that there is a resource showing apps that support one specific Lion feature; but an excellent starter source is Roaring Apps: http://roaringapps.com.

Roaring apps is a group sourced site that analyses apps and how well they do or don't work on Lion. This site had a lot more traffic right after Lion's release and I expect it to get hit again as (Redacted) Lion hits the streets.

It might be worth submitting to that site to see if they'd expand to cover Lion-esque features for more details.