I've read a couple threads recently asking if Greg Oden over Kevin Durant is the second worst draft selection in NBA history. There's an ESPN documentary out on Sam Bowie. I was thinking this would be a fun thread, especially because the Blazers made the right draft choice this year, and there's hope for this team now.
In my opinion, Oden over Durant wasn't even the Blazers' second worst selection ever, especially if you consider that Durant doesn't yet have a single MVP award or championship to his name.
Here are my rankings:

1. Drafting Sam Bowie over Michael Jordan
2. Drafting Wally Walker over Robert Parrish
3. Dafting LaRue Martin over Bob McAdoo or Julius Erving
4. Drafting Greg Oden over Kevin Durant
5. Drafting Barry Parkhill over George McGinnis

That list doesn't count Portland drafting Moses Malone then trading him for a draft pick that would turn into Rick Robey. It also doesn't count Portland trading the third down to the sixth pick, missing out on Chris Paul, Deron Williams and Andrew Bynum and instead taking Martell Webster.