If you don't have this DVD collection yet, you should definitely have it in your collection. It's got lots of great extras, including a letter from Joss Whedon to his Angel fans. I own this and I love it. You can get it used or new here on Amazon for the best price.
If you haven't watched Angel... why?? I know, people say it's not as good as Buffy. It's nothing like Buffy, so it's apples and oranges. I loved the show, but you don't have to take my word for it. Check out this great video from Passion of the Nerd... he'll tell you.