apache webserver and load balancer

[wcpav]

I am in the process of setting up two sun java system app server machines. The second machine works as a loadbalancer (and failover) machine to the first.
I believe, two webservers are necessary for the two appservers. Also, two load balancers (one as heartbeat to the other loadbalancer), one on each webserver machine.

So, there will be two appserver machines and two webserver machines. (the loadbalancers coexist with webservers)

Any suggestions regarding what webserver I should use? Is Apache free and available for interfacing with enterprise Sun Appserver? We are currently using sun web server. Is Apache better ... and is it good to use apache as webserver instead? If so, any specific version? Can someone also suggest a loadbalancer product that works with
apache webserver ....?

Any suggestions will be appreciated. Thank you.