As Lifehacker has this excellent post up on the subject, I won't bore you with my droolings, but will mention that Soluto is a nice way to shorten the time it takes for your Windows-based computer to boot.

Once you've installed the software and rebooted your PC, Soluto springs into action, tracking every single process that runs during the boot process, and then allows you to easily drill down into the list of processes to see exact times for each one.

To make it easier for the layman to understand what processes can be removed, the applications are grouped into "No-brainer" or "Potentially removable" groups.According to our conversations with Roee Adler from Soluto, the software will always be free for end-users. [...] Soluto's servers in order to analyze your system, but they assured us that it was limited strictly to data about the processes, drivers, and system components, and no personal information is transmitted or kept anywhere.

Here's a film from the company that makes Soluto, which explains all visually.