Gefen and Atlona make great quality scalers. I'm thinking of replacing my $60 upscaler (originally used for 16-bit consoles and my Gamecube).

I've never used a line doubler. It seems like it would work great with my LD player. But on the other hand maybe a scaler would work better.

I have a big Samsung plasma tv.

Thoughts?

A Line doubler is basically a low level scaler. It will just basically de-interlace interlaced video.

If you're plugging an SD source into an HD monitor/TV it's going to be scaled, even if you deinterlace it first. So your best bet is to use a scaler to do all that before you feed it to the TV.