There are probably all kinds of sweet tools available for testing performance. However, my main tool is the most user-friendly of all: my three year old Toshiba laptop computer. It contains a desktop computer grade 1.6ghz Pentium 4 processor with a very large cooling fan.
The laptop used to be my main workstation, but since I bought a new desktop machine it is mostly used for e-mail, chat, and light surfing. This doesn’t put a big load on the CPU, so I can browse most sites without the very noisy fan kicking in. This taught me most standards based websites are relatively easy on the CPU.
How do you test the performance of your websites?