Tastefully done graphic ads can be great for branding. I don't know how many of you have Chipotle's near enough that you see their advertising, but it's very simple and does outstanding branding. I'm very surprised that I haven't seen their ads start to pop up online. I think ads of that style can do a great job of building up awareness without annoying people to all getout.
(You can see samples on their web site: http://www.chipotle.com/
(click on play)
Audio ads seem to be the new pop-up. About.com started introducing them on their site when I was still writing for them and I HATED them. Now I get them all the time on some of the sites I frequent. (BabyCenter is a HUGE offender.) There's nothing worse than happily surfing away in a nice quiet room and then WHAMMO! Audio files coming from who knows where scare the heck out of you! It's obnoxious and unlike pop-up ads, the only way to avoid them is to turn your sound off. Personally, I like having my sound on, I might want to listen to a CD or something while I work and I do not appreciate having some audio ad superceed my CD while I'm browsing. :-P