A Playstation 3 VGA cable should suffice for your PS3-to-computer-monitor connection endeavors. I couldn't find it on amazon.com for some reason.

Assuming that your monitor is (or will be) connected to stationary computer, a TV card generally works fine for receiving television signals. I purchased a Hauppauge PVR-150 MCE card last year, which has aerial, S-Video and RCA (Composite) connectors for input. I have been successful in recording non-interlaced analog television signals with it, effectively storing 48 (50 for NTSC) frames per second, which is nice. The image quality is somewhat better on my CRT TV, but I cannot ascribe any particular annoyance to my TV card for this very marginal visual exacerbation. I haven't tried any HDTV-capable TV cards, so I won't say anything about those.

Anyway, the downside with TV cards is that the input signals will always need to be processed by a computer (usually the one which contains the card), which is the source of a minute amount of lag. This doesn't matter when watching TV, but it's notable when playing video games. The default input-to-action delay for my PVR-150 card was approximately two seconds, which I managed to ameliorate to circa 100 ms (0.1 seconds) after disabling post-processing effects (primarily interlacing) after some minor effort.

"Stephen Wolfram is the creator of Mathematica and is widely regarded as the most important innovator in scientific and technical computing today." - Stephen Wolfram