I've done this recently.
I use a Radeon 9600 ( vanilla version - not Pro or SE ) card and get an RGB signal direct from the VGA port going to my Panasonic widescreen CRT telly.
Apparently any 9xxx Radeon card will work.
You need to solder your own cable using an old SCART you dismantle, a phono lead, a VGA 15-pin adapter and a 75 ohm resistor. I bought all the bits I needed from Maplins.
You also need to install Powerstrip on your PC to get an interlaced custom-size widescreen resolution working under Windows.
It works a treat. The display is far better using the RGB than the Radeon's S-Video port. The only problem is the soldering is fiddly - you need a very small soldering iron. You should probably also get a multimeter to test your soldering before using the lead in case you fry your telly or graphics card.
Here are two websites on how to build it:
http://ryoandr.free.fr/english.html http://www.idiots.org.uk/vga_rgb_scart/
Use the pin connection table from the first site not the second.