It's a question I often receive from new photographers. Photographic equipment is very expensive, so it is understandable that people are interested in what works well and why. Equipment choice is an extremely personal thing and is ultimately more inconsequential to the final image than people often realize, but the following is a list of gear I have found useful:
1. Canon 5D Mark III
More than 95% of the images in my library were taken with this camera. The 5D Mark III has enough resolution for large prints of heavily corrected files. It's a large DSLR, but more convenient mirrorless cameras do not yet posses the battery life or perspective control lenses required for serious architectural photography.
2. Canon TS-E 24mm f/3.5L II
This is possibly the best lens Canon makes. It's manual focus only since it is a specialized lens that physically tilts and shifts, but no amount of Photoshop wizardry can replace the ability to control perspective in camera.
3. Canon 16-35mm f/4L
A versatile wide angle lens is convenient for small home interiors when you need to be in and out quickly. There's a significant amount of barrel distortion, but it can be almost completely removed with a good lens profile.
4. Canon 70-200mm f/2.8L II
Architecture is primarily done with wide and normal lenses, but a short telephoto lens is great for exterior details of large buildings. It's extremely large and heavy but has great contrast and sharpness.
5. Canon 24-70mm f/2.8L II
I don't use this lens for architecture because it has a large amount of distortion, but this is mounted to my camera for nearly everything else. If I could only have one lens for a wide range of photography this would probably be it.
6. Manfrotto MT055CXPRO3
Every serious photographer needs a tripod. The Manfrotto is extremely stable despite its light weight.