Which Firewall i can use with Avast! free antivirus?(Except Windows Firewall)Any sugesstion? 
Any hardware firewall can be used and about all (free) software firewalls.
Name any of those?
the least complicated, Windows firewall and turn on your router / ISP box firewall if not already on
Be Secure…
You could always try the “best” free firewall…
The Comodo free firewall link is soooooo long, I had to use the “tinyURL” site to shorten it. 
Been using Comodo for years & never had a problem with either it or getting anything nasty on my M/C.
It does exactly what a good firewall should.
Stay safe.
Comodo ships Adware Privdog worse than Superfish
https://blog.hboeck.de/archives/865-Software-Privdog-worse-than-Superfish.html
http://www.ghacks.net/2015/02/23/privdog-is-superfish-all-over-again/
Be Secure, Google is your friend. Search “Free Firewall Software”/and Reviews.
Do some research, and you’ll quickly get to know what’s available.
As far as commonly used Free Firewalls by Avast users here on the Forum, Ive noticed these:
OutPost FW
Private FW
Comodo FW
and there’s others.