Can't find Angry Birds
GetJar is where they first posted it and it got hammered. They got it on the Android Market pretty quickly, but Rovio's complaint (and why they went with an alternate market in the first place) is that a lot of people complained they couldn't find the beta in the Android Market.

A few people who were able to get it set up mirrors, including a Torrent. A quick web search should find an alternative download location for you, if you haven't already got it.