Just read about the Pound Loadbalancer for web traffic; although I've not implemented it, it looks slick.

What do you guys use for load balancing apps (not just web)?

We use a hardware load balancer. Honestly it's the only experience I have with one. Like most commercial products, the docs suck, but after pouring over them for a long time, it is a flexible piece of equipment. It's a Foundry Network Serveriron switch/lb. - nathan