You are getting close to the CAUSE of why you swing your left leg out to the right.
The CAUSE is that you are not throwing your body sideways up and out at the ball - "cartwheeling" sideways as you powerfully "reverse the bow".
You are mainly swinging your shoulders from left to right (uncoiling) - and while that is good - you are not "dropping your left shoulder" as in the following video:
Preventing Rotator Cuff Injury TennisOne.com Editor Jim McLennan explains some serving techniques to generate power and protect your shoulder.
http://www.youtube.com/watch?v=lTRvxaBMh8s
This is what "dropping the left shoulder" looks like at impact:
"Dropping your left shoulder" will allow you to throw yourself sideways up and at the ball and subsequently into the court.
Setting this up by getting your body more into a "bow shape" at the trophy position is necessary to then forcibly "reverse the bow" and throw the side of your body "up the mountain" at the ball, and subsequently straight forward into the court, and not falling off to the left side as you are currently doing.
Here is a video of Soderling serving. It is easy to see how powerful his bow shape is, and how he explodes out of that position:
http://www.youtube.com/watch?v=a56pvP1i6x8
Note that "leading with the left hip" is necessary - the left hip must move out over the baseline as you form the bow shape to counterweight the tilt back away from the baseline by the upper body/shoulders:
Tennis Lesson: Serve Tips: Lead with the Hip
http://www.youtube.com/watch?v=HgeYmEScfgQ
All of this is emphasized in Nick Bolletierri's video, Sonic Serve:
http://www.youtube.com/watch?v=ajoZ0f7hw-A
If you can incorporate that more pronounced bow shape in the trophy positon, you'll look more like Pete Sampras in pic 1 of the sequence below:
The force of Pete "cartwheeling" sideways into the ball includes dropping the left shoulder" so that at impact in pic 7 his left shoulder is straight down, and his right shoulder is straight up.
The force of this powerful "reversing the bow" motion throws Pete straight into the court, not to the left like you.
So when you learn how to powerfully "reverse the bow", you'll also have to learn how to land on the left leg, and kick straight backward with the right leg:
Leg kick on serves from Fuzzy Yellow Balls:
http://blip.tv/fuzzy-yellow-balls/leg-kick-on-tennis-serve-1190196
[You'll know you are doing it right if your leg is moving straight back as a reflection of you moving into the court.]
[You comment on your "high" toss - note that Sampras's toss was about 16 inches above the contact point, and most pros toss about a foot above the contact point.]
[Note that you can see that Sampras has a powerful coil/uncoil motion just like you.
But his bow/reverse the bow motion is so powerful that it overpowers the spinning to the left that you exhibit, with instead the net direction of the leg and body movements is first up and at the ball ('up the mountain") with his body follow through straight into the court.]
I hope this helps.
Good luck!
[P.S. If you post more of your serve, could you also post a view from the side?]