Utils
Duplicate Cleaner - http://digitalvolcano.co.uk/dupe.html - finds duplicate files, and has handy options to auto-select which set to delete
TextCrawler - http://digitalvolcano.co.uk/textcrawler.html - find and replace across multiple files/folders, including a RegEx engine
Unlocker - http://ccollomb.free.fr/unlocker/ - remove a system lock on any file
Comodo free suite - http://www.comodo.com/products/free_products.html - free anti-virus, firewall, anti-spam, anti-malware, and a backup/synchroniser
TrueCrypt - http://www.truecrypt.org/ - creates a virtual encrypted disk within a file and mounts it as a real disk, with a 512-bit key