I love Monoprice.com, their cables are pretty awesome. Almost every cable in my setup comes from them. In fact, when one of my HDMI cables starting acting odd, they replaced it for free, I didn't even need to send the old one back, they sent a brand new one right away. Their prices are very affordable too, so it doesn't hurt to stock up!

On my current setup I have my LD player sending out it's composite video signal to my DVD Recorder, which is connected to my TV via component. I have not seen an advantage to S-Video when I have my LD player connected, however when I have my JVC S-VHS deck setup using S-Video it looks beautiful!

The best cables that I've used and still do are Transparent Cables but be prepared to spend a arm and a leg for them.
A pair of my speaker cables are $1000 and that is on the low end, I've seen the top of the line cost over $10,000.
I have invested at least $5000 on cables and do they make a difference? My god they do, the sound quality is incredible.

I try using cables as short as possible. I found cable length can be an important factor.
Not using (European) scart output myself. I use the composite out with an AIV 75ohm composite shielded cable. Does make a BIG difference in my setup when comparing with yellow standard cinch plugs.
for optical output I use the bandridge or Profigold cables altough I can't tell any difference in audio quality when compared to a cheap optical cable.
I believe when using a mid quality cable it all schould be ok.
Avoiding cheap cables can make a difference in any setup.
Depending on how different brands work together results can be surprising.
I like Philips displays and dvdo de-interlacer chips . Combined they make a great picture with laserdisc.
Activating minimum DNR on my Philips display receiving a Yuv signal looks great. sturdy picture at 480p from receiver.
S-video is ok when used in my setup but I much prefer the composite out look. I've been playing around with my display settings for some years now and am satisfied with the results. I avoid using the HQ button on any ld player!

Bottom line for me,
Middle class cables and you can't go wrong
From that point on it only can get better...

My Tv cannot display S-Video, either the picture gets black&white (obvious incompability with NTSC) or it's just filled with noise. However, by combining S-video and composite, the picture looks wonderful. I've never thought of trying out some expensive cables though, I'm not so picky about picture quality.

Does the length of the cable play a factor in it?