Standard DVD is an option, but not a good one. They are very easily destroyed by casual use and can only hold 4.7 GB. You would then have to store them in a special location like you did with the memory cards. Some Mini DV tapes can hold 11 GB of footage, so you can see how replacing a single Mini DV tape with a DVD may not be the economic video storage choice.
A new disc format that is emerging is the Holographic Versatile Disc and it tries to put 300 to 500 GB on a disc that is the same as the one Blue-ray uses. They have promised to eventually be able to store anywhere from 3.9 to 6 Terabytes on them and hold a transfer speed that is around forty times what DVD is holding. This is just an emerging technology and it may take time for the price and technology to be practical for most people.
Blue-ray still holds 25 GB on a single layer disc and 50 GB on a dual layer disc, and is the primary format for HD video. The problem with all disc technologies is that have organic dyes used in storage and they can fade over time. This puts them in the same category as raw color film, which degrades.