Some Good Sites to Check for Malicious Content

I really like McAfee's and BrightCloud located at I paste the ip that I think is bad or malicious into their reputation database. Then I can block accordingly in my firewall. To look for a particular ip address in your apache logs type the following.
grep {ip} /var/log/httpd/*

Typically your apache logs are all located in /var/log/httpd/

I also like this site. If your business does not need access to overseas or no one needs to connect to these netblocks you can use these in a block list as well.