Sumatra PDF is a free PDF, XPS, DjVu, CHM, CBZ and CBR reader for Windows.
Sumatra PDF is small and starts up very fast.
Simplicity of the user interface has a high priority.
Portable version included (a single executable that can be run e.g. from USB drive and doesn't write to registry).
http://blog.kowalczyk.info/software/sumatrapdf/download-free-pdf-viewer.html
HelderC