OSS + high traffic to IIS http servers

Several clients running IIS webservers (supposedly) are expecting a (i.e. free!) solutions that I might use to effectively deal with the bandwidth issues. (They're heavily invested in .NET on the backend, and it's not my decision to change anything -- just make it work well during times of high traffic.)

Over the past few weeks, I've been working a lot with F5's BigIP, which has some incredibly cool features for properly filtering load balacing OSI layers four through seven. The problem with their solution(s) is the price: every single cool feature is a software module that costs a lot of money.

version of Red Hat 7 or something, so why not build an OSS ver? For something simple like load balancing, I suppose that i could just use Pound. For caching, I have options like squid cache, etc. What other open source solutions might I want to start investigating?

On a somewhat-related note, what stress testing tools can I use to see what a webserver's response time is? It's tools like this that will hopefully help me determine other n-tier solutions I need to think about. (Yesterday I played with Siege. It blasts a website with a whole bunch of traffic and then reports back your response time.)