There are lots of options here.
Amazing Charts offers an offsite backup service for $250 a year.
If you choose to do it yourself you need to backup the
*.mdb
files in the amazing charts folder.
Personally I use smart sync pro, which is $35 one time fee.
http://www.smsync.com/I back up to several different computers on the network and several USB drives (which some I rotate offsite) on varying schedules, keeping multiple multiple copies of old files. Be sure to choose the copy source to destination option and not synchronization.
For offsite backup I use MOZY,
www.mozy.com This service offers both a free version (2 gigabyte) and pay version (30 gigabyte) for $5/month.
You have the option of supplying your own encryption key and they offer 414 bit encryption so files should be very safe. You can set it to automatically backup every evening.