The shaker is the most essential of all the tools a bartender uses. There are two kinds of shakers, Boston Shakers and Cobbler Shakers. The Boston Shaker is superior of the two but it's slightly more difficult to use.
This shaker is well priced, has a leak free seal, doesn't rust easily, and already comes with a well fitting strainer which is a nice bonus. Another nice touch is the drink recipes found on the side of the glass itself.
I highly recommend you take on the minor challenge of learning to use a Boston Shaker but if you'd like to stick to the more beginner friendly Cobbler Shaker, I'd recommend this one.