Performance and Capacity

ATL-CSIM: System Simulation and Modeling Tools.
Lockheed Advanced Technology Labs' CSIM is a general purpose discrete-event simulator for block diagram oriented systems. Graphical/interactive or text/batch simulations. Not to be confused with Mesquite Software's CSIM18, another simulation tool.
http://www.atl.external.lmco.com/projects/csim/

Quantitative System Performance
Introductory text on analytic computer performance models. Complete text is available as searchable PDF. Published in 1984.
http://www.cs.washington.edu/homes/lazowska/qsp/

Speed Up PC Performance
Modem tweaks and browser tips to speed up Internet access. Reports web accelerator software options which claim full optimization.
http://www.speedupnow.com/

Stratton & English Software - Performance Specialists
Provider of Internet Software Services, specialising in Performance Investigations - including performance prediction, optimisation and testing.
http://www.strattonenglish.co.uk