After a morning of clicking around, I've settled on the 2011 Masters Tournament leaderboard at Yahoo! Sports as the one I'll most likely stick with for the rest of the tournament when just looking to check scores. It loads quickly, updates itself frequently, and really doesn't have anything going on that gets in the way of the information.
Then there's the live leaderboard at Masters.com. Like everything else on the site, it's very stylized and operates according to its own rules, which is at least very Augusta National of it. But compare the look of this leaderboard to the simple lists of scores provided by most others. It's meant to look like the actual leaderboard at the course, and it does, but it's not easy to read in two seconds or less unless you've adjusted to it.
Links to live video redeem the official leaderboard, but you can get the same video at CBS Sports' leaderboard with an overall better presentation, though it has ads.
ESPN's Golfcast includes a live text chat with David Kraft and a nice hole-by-hole list of live results that I haven't seen anywhere else. It does autoplay an ad upon loading, so turn down the volume if you're at work.