Additional from above tools:
TrueCrypt (not open source, but free):
TrueCrypt (Windows Vista/XP/2000 and Linux) (encryption)
Open source alternative to Roboform:
SourceForge.net: KeePass Password Safe /
KeePass homepage
Advanced users can check out Core Force firewall:
Core Force Firewall
... needless to say, you should have a properly configured hardware firewall (in addition to your software firewall) and anti- virus/trojan/rootkit installed as base.