Sagittarius and Aquarius
This is a surprising combo because the Sagittarian fire heats up Aquarian coolness, and Aquarius feels comfortable with Sagittarius's integrity and easy good nature. The experimental side of Sag finds a willing partner in Aquarius. The only drawback is that, when Aquarius is turned off, Sag will become frustrated by his inability to get things going. Sag does not have energy dips the way Aquarius does, and will take it personally if the lights go out. The absolute assurance between Aquarius and Sag that no one's freedom will be curtailed by a liaison between them is a great turn-on.