Best way to store videos from a full DVR?

If you keep saving videos on a DVR, it eventually becomes full of course. What's the best way to store videos recorded on a DVR that you would like to keep and to free space on the DVR. I know you can buy a supplemental DVR, but on my system (Cablevision with a Scientific Atlanta Explorer 8300 DVR), the DVR is tied to the specific new DVR (i.e., no other DVR can replace it and only that one extra can be used). What's also bad is that if you move, you have to get a new DVR. I know because that happened to me. The DVR is convenient to use and gives a clear picture. I can transfer stuff from it to my VCR with no problem (except that it's tedious), but VCRs don't give as clear a picture, are inconvenient to use (winding and rewinding), and the tapes take up a lot of space. Can you transfer a video from a DVR to a DVD recorder? I've heard that there's some that cannot be transferred. Is it complicated to do or can you just hook up the DVD recorder inline after the DVR? Or is there some better method? Anyone have any thoughts about what is the best way to resolve this problem?