L lenses are all full frame, so they are somewhat overkill for a crop body.
I like to balance quality of the lens with the body. With a 750D, virtually any lens can take beautiful photos, its just a matter of what focal length and aperture you need.
If you really want a "L" lens anyway, you might get a 16-35mm F/4L or f/2.8L for normal focal lengths. A 24-70L for slight telephoto, and a 24-105mmL for walk around slight- moderate telephoto use. For wide angles, you are better off with a EF-s lens intended for wide angle on a crop body. A 70-300mm L makes a good telephoto lens for crop bodies.
Sometimes we tend to forget that the skill of the photographer is by far more important, no amount of expensive gear will make him better. I'd start with the inexpensive kit lenses and find out what you feel is needed for the type of photography that interests you. You can buy used, and resell if you decide to get a expensive lens.
For wide landscape shots I would recommend the EF-S 10-22mm, for better range of zoom covering wide to mid range, the EF-S 15-85mm, for lower light levels, the EF-S 17-55mm f/2.8, this lens is said to be “L” quality, but Canon wont put L on an EF-S lens.