I love it when beer bars list their current offerings online; conversely, it's frustrating to go to a place specifically because they listed online something you wanted, only to arrive and find out the tap list was outdated.
I was in LA a couple of months ago and spent one evening after work at the Blue Palms Brewhouse. They update their beer menu on a computer at the bar, and project the list onto the wall above the bar. The same list is published to their website. You know for sure, by the minute, what's available. Check it out - it's a pretty cool menu approach.
Free State does a pretty good job of staying current, but it seems they switch out kegs so frequently, it'd be hard to keep their website current unless they updated it daily. They do, however, tweet every day about their daily food specials and when new beers go on tap. I'm not a fan of having to scroll through their tweets, so I usually just call them. There's almost always at least 1 beer they mention on the phone that isn't on their website. Beer Kitchen has been doing a great job of ensuring a current beer list, as is the Foundry. Until recently, Waldo Pizza just threw out general logos on their beer page, and most of them weren't for beers they currently had. Now, however, with their updated website, they give you a full PDF download of their entire - and current - beer menu. (which, by the way, contains some pretty great beers right now - Expedition Stout on tap!)
I hate having to call and ask what's on tap, and I'm sure employees find it a pain to have to track down someone who can answer my question. Kudos to those bars & restaurants who put forth the time & effort to keep an online beer menu that's up-to-date and reliable. To those places that don't publish tap lists online - please consider doing so. It can't be too hard to update at least once a week, and does have an impact on a beer lover's decision to visit your business.