That's not a very "scientific" way of putting it, but it's obvious what you mean. The answer is Uranus.
Uranus
The planet Uranus is tilted "on its side" about 98 degrees to the orbital plane. But all planets in our solar system have some tilt to the side, including Earth which tiles about 23 degrees. (Mercury's tilt is very small.)
There are 8 planets in the Solar System. (There use to be 9 total planets in the Solar System) The planet that is tilted on its side at 98 degrees is Uranus.
Uranus is the sideways planet in our solar system.
There are about 408 multiple-planet solar systems in our galaxy. The orientation of these solar systems are on a flat plane due to lacking giant planets, where as ours is tilted off the solar system's plane because of Jupiter's gravitational influence..
Neptune is our 8th planet in the solar system!
Earth is the strongest planet in the solar system
8th planet in the solar system
Venus is the hottest planet in the solar system
The largest planet in our solar system is Jupiter.
The biggest planet in our solar system is Jupiter.
Yes it is, the largest planet in our solar system.