I'll detail my exact setup below, but general recommendations for a better web-browsing experience will be useful. A nice checklist of things to try would be great!

I have 600 users on a single site with an 8MB leased line. I get a lot of moans about the performance of "the internet" (ie web-browsing). What recommendations do the community have for speeding things up without just throwing more bandwidth at it? I expect I will end up buying some more, but good management tips are always valuable.

My setup is this: Cisco PIX (515E) firewall on the edge of the network. It's just doing some basic NAT, and opening up a handful of ports to various bastion hosts (aka DMZ servers).

The DMZ is just a switch that the servers are plugged into.

ISA 2006 Enterprise array (two servers) connecting DMZ to the internal LAN, with WebSense Web Security filtering HTTP traffic so users can't look at porn or waste bandwidth on YouTube during working hours.

I've done a few things - I've just switched my internal DNS over to use root hints, which halved DNS query latency from 500ms to 250ms. Well worth doing.

I'm trying to cache more aggressively, but so much more of the internet is AJAXy and doesn't cache very well as compared to five years ago. Plus the 70GB of cache which felt like a lot a few years ago really isn't any more. I'm getting about 45% cache hits by number of requests, but only about 22% by size, ie larger objects are less likely to be cached.

Latency seems to be part of the problem. Is that attributable to the bandwidth problem, or are there things I can look at to try to reduce latency even on heavily-loaded bandwidth?