A while ago I saw a video on Picture Correct and I had to try this myself. I really loved the good tutorial by Gavin Hoey as he explains everything very well!
The equipment I used for the Photo below is:
The lens has a nice wide angle which helps a lot for this picture. If you don’t have a very wide angle you just have to take some more pictures.
The disadvantage of the Tripod I have, is that it has a ball head which rotates in all directions. It’s not possible to lock the camera vertically and only move it horizontally. It helped me for this picture to keep the horizon in the finder window on exactly the same position. Small errors are luckily fixed by Photoshop, so you don’t need to buy a new tripod(head).
The result:
