Mod me redundant as this has been said already, but this is my personal strategy:
1. Cull photos. If you do serial shots take time before the 1st backup to delete the duplicates. Also, be strict to remove all shots that are not perfect technically, unless their composition or motive is really outstanding.
2. Tag photos. No point in having an archive of 20000 pictures if you can't find them.
3. Back up. As said elsewhere, external disks are cheap. Make sure you have multiple backup disks, and store them physically separate.
4. Use online services. A Flickr pro account is $25/year and allows you unlimited uploads. Backup everything to Flickr as private pictures in the original resolution, then share what you want via guest passes. It may take hours or days to upload a batch of photos, just let the computer do it overnight.