I'm surprised no one has mentioned this one.
https://www.youtube.com/watch?v=CIskk4e-noM

that was my second choice.

Top Ten...? No, there's two :D

http://www.youtube.com/watch?v=fOdq0g0YPRQ

http://www.youtube.com/watch?v=geiM-sY12v0

Sambasaurs and cute earth elemental angel girl. Nice

The Nossan and the Earth Angel! (Song Title Reference!)

Gokai Change!
http://www.youtube.com/watch?v=x_Wd2y_Mlbs

Part of me wants to go with my sentimental favourites like the intro to Liveman, Jetman, or Dairanger, but as a combination of that and the fact everyone picked the best ones, I'll suggest these two . . .

SAAAAAVE THE EAAAAARRRRRH . . .

http://youtu.be/y3sB6-MnJng

Given the show it's based on, it's approriately ferocious, especially the guitar solo in the middle.

http://youtu.be/hR7ftRGYsOg

Matrix is posting!
Place your bets! Is he gonna post Geki's intro?
...
The tension!
...
"It's gonna be Geki. It's always Geki." -Everyone
...
"Why is he prolonging it? It's obviously Geki." -Everyone else.
...
...
...
You sure?
:p
http://www.youtube.com/watch?v=ck1SLwIIhnI
Nope! Secret Kakuranger!

But, I gotta give a shout out to Dairanger's opening!
http://www.youtube.com/watch?v=U8GQhvI2-N8
RyuuRanger! ShishiRanger! Tenma! Kirin! HouohRanger!

...
*Coughs*
http://www.youtube.com/watch?v=LEVXJDh3_NY
*Winks*
http://i.imgur.com/W4jzZOT.png

In third place, we have... the POLICE
http://www.youtube.com/watch?v=TFqJQX9N7Ps

In second place, DINOSAURS!
http://www.youtube.com/watch?v=zXuhsa686Ls

And, in first place, a surprise entry!
http://www.youtube.com/watch?v=u4CCvlob4ok

Honourable mentions go to Tensou Sentai Goseiger and Gaoranger

1. Samurai Sentai Shinkenger
2. Kousoku Sentai Turboranger
3. Denji Sentai Megaranger
4. Jyuken Sentai Gekiranger
5. Choriki Sentai Ohranger
6. Tokumei Sentai Go-Busters
7. Hikari Sentai Maskman
8. Chojyu Sentai Liveman
9. Engine Sentai Go-onger
10. Taiyo Sentai Sunvulcan