Encode HD video to a good format for editing
What you are looking for is probably a so-called intermediate codec that is specifically targeted towards editing. It will allow you to perform a (visually) lossless compression but still make changes to the video without reasonable quality loss. Just like JPEG isn't made for resaving a photo a hundred times, you will need a special codec.
Your approach with DV wasn't that bad. The only problem is that the DV standard only specifies a maximum resolution of 640x480 pixels.
HuffYUV
I'd suggest you try HuffYUV, which is a lossless codec that is relatively fast and should be easily editable on Windows platforms. On Linux and OS X it's not the best choice though. ffmpeg has HuffYUV support built in, so you don't need to install anything else. You can try something like:
ffmpeg -i infile.mov -vcodec huffyuv -acodec copy outfile.avi
You shouldn't need to specify the frame size or anything. Just give it a try. The advantage is that it saves the video frame-by-frame, which is what you want for editing.
MPEG2
Another alternative is to convert to MPEG2 using only intra-coded frames. Intra-coded meaning that every frame is fully coded. MPEG2 is not really that useful as an intermediate codec, but it's still used for professional video transmission and storage.
ffmpeg -i infile.mov -vcodec mpeg2video -qscale 1 -qmin 1 -intra -an outfile.m2v
Note that you could get a really huge file. MPEG2 should be easy to edit though, as it's a very basic codec.
DNxHD
DNxHD is a visually lossless intermediate codec by Avid. There are ffmpeg versions that can encode to DNxHD. For example, ffmbc is a specialized ffmpeg version targeted towards video broadcasting.
ffmpeg -i infile.mov -vcodec dnxhd -b <bitrate> -an output.mov
See this table for bitrates to be used. You might not be able to open the result file with every editor. You'd also need to have the decoder plugin installed. I've personally used it with Premiere Pro on a Mac and it's a really good codec.
If you have any issues, let me know.