Panda USB Vaccine is a free utility from Panda Security Research which helps prevent malware infections due to the autorun

USB Vaccine allows users to vaccinate their PCs in order to disable autorun completely so that no program from any USB/CD/DVD drive (regardless of whether they have been previously vaccinated or not) can auto-execute. This is a really helpful feature as there is no user friendly and easy way of completely disabling autorun on a Windows PC.