Linux Firewall + Loadbalancer distribution

The opensource firewall pfsense can do load balancing (see the link). They have a VMWare appliance. You can buy commerical support etc. It's based on FreeBSD though so if you have some absolute requirement for it to run on Linux then it may not be suitable.

I don't know of any (but I haven't really looked either) distributions that specializes in these unless you want to start paying some money. (F5 LTM for example). But any decent linux distribution can do both of these things easily. There are lots of free load balancing apps out there that run on Linux:

http://haproxy.1wt.eu/
http://www.ultramonkey.org/
http://www.linuxvirtualserver.org/
http://www.inlab.de/balance.html

And the firewall (iptables) part is just part of any standard Linux distro. There are also lots of apps out there to help simplify configuration of this too.