Crawl Log Error: An unrecognized HTTP response was received when attempting to crawl this item. Verify whether the item can be accessed using your browser.

My farm configuration: 

3 F5 load balanced WFE's

2 query servers

1 dedicated wfe <also my Central Admin server>

1 Indexer

Search seems to break everytime I sneeze this one was resolved quite easily although I can't tell you yet why it broke.

Resolution:

1. Go into the indexer and save the host file contents to host-backup and delete all of the contents <timer job should replace within 1 minute>

2. Go into your browser on the indexer and go to Tools--> Internet Options--> Connections--> Lan Settings

Check the box in Proxy server and put in your proxy server.  Check the box for Bypass proxy server for local addresses. Click advanced and put in *.yourdomain.com.

This may not work for you but it finally worked for me.