The next best Canon lense

[kenb]

The Canon 15-85 lens hasn't been mentioned yet - it has a very nice range and sharpness and is extremely versatile. Only thing it lacks is a 2.8 but you can't have everything!

[DanK]

I think you have two kinds of advice here: 1) don't buy anything yet, vs. 2) buy something now (50mm, tripod...)

I'm with Donald, Richard, and Glenn: don't buy anything until it's clear to you what you want to do that you can't do well with your current gear.

I am into landscape photography, which includes wide mountain ranges, but also getting up close and personal with flowers. I also like taking pictures of wildlife, and of course my dog.

As Glenn pointed out, no lens is good for all of these. So practice more, and see which of these becomes most important to you, and for which of them your current gear is most limiting.

Re the suggestions for a 50mm prime and a tripod: I would put these off for the same reason. Tripods come with a bewildering array of features, so you need to know what you are going to use it for and what features fit your particular style of shooting. For example, I use a completely different type of tripod head for macros of flowers (a heavy geared pan and tilt head) and for landscapes (a light ball head that I don't mind carrying on my back). Ditto, for the 50mm: you have not given a strong argument for it. For some people it is a good move; for others, not. (I shot with only primes for decades, and a 50mm was my standard lens for the years I had 35mm film cameras. On a crop sensor camera, however, I don't find it a particularly useful focal length, and I don't even own one that will fit on my current camera.)

So practice, and when you find something you really can't do (see Richard's list), then it will be time to buy.