this is kinda the point of disk encryption dude... keep the files locked away from the bad guy...
If this is a personal computer then Bitlocker is fine, If this is going to be more of a corporate managed machine, you can go with McAfee End Point Encryption, Credant Manager, Credant Shield, DDPE (Dell's software based disk encryption), Sophos was mentioned, TrueCrypt...
you should stay away from the cheap encryption "freeware" type of products just out of security reasons.