Here are two free cloud-based antivirus which have been found to work satisfactorily alongside cis.
1.Hitman pro 3.5 ,It somehow combines the detection technology of several engines like avira ,a-squared,nod,prevx,gdata to analyse suspicious files. Free unlimited scan.(note removal is not free after 30 days but well it's a good start
2.Immunet cloud-based antivirus. Developed by former director of symantec and Mcafee executive . Seems even to integrate with social networks like facebook to form small communities and enhance protection. It not only protect your pc but protect the cloud as a whole .Best of all it is free,has a fast scan rate and is compatible with cis ( i am testing it right now and the founders recommend not to uninstall your current antivirus if no incompatibility issue is found).http://www.softpedia.com/get/Antivirus/Immunet-Protect.shtml
Check these 2 and leave feedbacks.