Fluorfinder 2.0 - An invaluable tool for all users of flow cytometry to design a superb, working antibody panel. The website is tailored to the instrumentation located at Brown University. Requires free registration.
BD Spectrum Viewer - This is an excellent tool to help with antibody panel design.
Flow Wiki - Basic "What is flow" information
Purdue Cytometry Discussion List - A forum of flow cytometry talk for advanced users.
FlowJo - Analysis software for flow cytometry (Mac, PC)
Flowing Software - Free analysis software for flow cytometry (PC only)
Affymetrix eBioscience Compbeads - Compensation control beads for complex panels. Allows compensation of fluorochromes using beads rather than cells.