I recommend these two lenses to any photograher with the budget. I am providing Canon info and Nikon info as well as links to Pentax and Sigma.
Reason: The wide f2.8 max aperture of this lens means that its perfect for shooting in low light situations. The focal range of 70-200 is perfect for gym sports, hockey, weddings and I even use this lens for most of my portraiture.
Price Range: Expect to pay $1800ish for Canon Brand. $2800 for Nikon Brand. $2300 for Pentax Brand and $1700 for the Sigma versions (March 2020)
Recommendation: The 24mm 1.4 is a beast. The f1.4 max aperture allows you to shoot night skies and low light situations with surprisingly fast shutter speeds. NOTE: I am only recommending this lens for full frame cameras.
Reason: This is a lens that changed the way photographers shoot the night sky. It is sharp at infinite, even at the f1.4 setting (often super wide aperture lens can tend to struggle for sharpness). If you plan to shoot lots in low light then you must have this lens.
Price Range: Expect to pay $2500ish for the Nikon Brand. $2100ish for the Canon Brand and $1100 for the Sigma Versions (Oct 2018)