I pondered about the options too!
There is the Option of a laptop having a DVD-burner, that would relieve you off 5GB per DVD plus I don't think the DVDs will be stolen (at least if you do seperate them from your valuable equipment!).
The other Option is an external 2,5" hard disk USB drive (Trekstor USB-Storage DataStation pocket x.u). I just bought one with 160GB for around 130€. This is a very small and light box (12x8x1,4cm, 160g) but 160GB is the max you can get them today. That may be to small for your requirements, esp. if you like to preserve RAW files (@10MB each) like I do, but there are the larger capacity 3,5" USB-drives with capacities of up to 500GB (equiv. of 42000 photos in RAW+medium jpg). They are cheaper (per GB) but need a little more space.
There are some options that take the SD card directly and make back-ups directly, no laptop needed. BUT
I know of no gadget of this type that can read the new SDHC standard that the D80 supports for mem cards above 2GB (see my profile). AND
without laptop you have no chance reviewing what you've got!
When calculating the amount of space you'll need here is just one personal experience: I once visited Istanbul and found myself shooting over 100 pics per day. So if you're running around like that you end up with 3,000 pics per month i.e. 27,000 pis at a 9 months trip
If you try burning this on DVDs in RAW quality you will need almost 70DVDs