My favorite large ruler is the Wrights EZ ruler. It's 6-1/2x24", clear plastic with thin black lines. To me, Omnigrid/Omnigrip rulers are really hard to see through on any fabric. My Wrights ruler gives me no trouble, not even on black fabric (which I use a LOT). I bought it at Joann's. I love it so much I bought a spare!
I also have a large gooseneck lamp that arches over my cutting table with a "daylight" spectrum bulb in it, so I have very bright light that shines directly down on my cutting table. That makes a HUGE difference - even during the day when the room is pretty well-lit naturally, if I switch on that lamp I can see EVERYTHING. And the light comes directly down where I cut, not at an angle, and I think that helps with cutting accuracy too. No shadows being cast an an angle from the cutting lines on the ruler...
Someone else mentioned Creative Grids rulers - those are great rulers too.