When to use a load balancer?

I currently have a single dedicated server for my website but traffic an bandwidth will eventually because a problem. I was just wondering what other webmsters use in terms of server/load balancer configurations.

I've heard that some high traffic websites use a load balancer, several servers for the web application(s) and a database server.

What server configurations do you use?

Thanks,

G

Slashdot just ran a couple articles on this subject for their 10 year anniversary this month.

Part 1: Slashdots' Hardware
Part 2: Slashdots' Software