It can be really hard to optomize, since art-direction in games these days never seem to take HD into account.
But if you're jumping back'n'forth between progressive and non-progressive games keep the 'sharpness/picture' fairly modest ---- on my samsung I crank it at about 40% since I play a lot of RE4, and games that run less than 32bit colors can really get muddy the sharper you get.
But if you're running games like MarioKartDD, you can crank that sharpness like a biyotch!
In general most first-party GC games look outstanding, something about the component-cable on the cube --- that and many run at a solid 60fps.... with my experience progressive is all for not and hardly noticable without 60fps.
If you're runnin' that lower sharpness, then go ahead and turn the 'digital-noise-reduction' off --- This keeps settings good for PS2 non-progressive.
Keep the Brightness more like movie-standard --- where the screen never totally goes to full-black. In other words, make it to if there's nothing but black-void on the screen - there's a slight slight neutral glow from the screen, and not total darkness.
After that, cut your contrast a few hairs above that brightness.
This will be easy on your eyes, since many many games run too dark for their own good --- and also this'll be easy on jaggies, and in general avoid a muddy image.
Color can be tricky, since there's such a huge range in games today - so look at what you're playing ---- pop in Pikmin2 and make sure the colors don't blow the eyes out the back of your head. (actually, i found that Pikmin2 was a great HD test all-round since it's a game that needs a much higher resolution than it's given)
But I keep my color a little toned down, since most games today (even if they're going for a dessaturated color-palate) get way to saturated for their own good, since they're usually trying to show off their textures more than create a nice mood.
A great TV can make good grey-tones look damn sexy too
But do some tweaking, and have some fun getting obsessive since there really is no 'standard' as of yet.