Source: WordPress.com
To embed the YouTube video with default width and height adapted to your theme:
[youtube=http://www.youtube.com/watch?v=e5cfyAt-0rU]
To specify the width and height explicitly:
[youtube=http://www.youtube.com/watch?v=e5cfyAt-0rU&w=320&h=240]
To specify the width only:
[youtube=http://www.youtube.com/watch?v=e5cfyAt-0rU&w=320]
To hide the related YouTube videos from appearing after the video is done:
[youtube=http://www.youtube.com/watch?v=e5cfyAt-0rU&rel=0]
To start at a certain point in the YouTube video, convert the time of that point from minutes and seconds to all seconds, then add that number as shown (using an example start point of 1 minute 15 seconds):
[youtube=http://www.youtube.com/watch?v=e5cfyAt-0rU&start=75]
To specify a start and end time for a YouTube video, do the same as the above but add the end time as shown: [youtube=http://www.youtube.com/watch?v=e5cfyAt-0rU&start=75&end=85]