ONLY the series that started after the show finished are canonical in the show's timeline. since buffy and angel are in the same universe, that means the timeline is made up of the following:

buffy
angel
buffy seasons 8 and 9
angel after the fall (occurs at the end of angel -- it's a bit fuzzy here because joss was only attached for the first arc of the issue and he seems to be ignoring everything that happened after he left, which is ok by me because it sucked)
angel and faith (occurs concurrently with buffy season 9)