Home plate
This is an obvious piece of equipment.  Having a home plate available allows the hitter to align themselves up and maintain a proper hitting stance.  Effectively used for soft toss drills or actual batting practice from a live arm or pitching machine.

L-screen
An L-screen is simply that – a screen in the shape of an L that allows the pitcher to throw batting practice while providing protection from line drives.  If you can afford one piece of equipment then this would be the one to buy.  Having an L-screen will not only provides protection it will fully allow you to maximize the size of your batting cage.  You can place the L-screen closer to the hitter while still maintaining a very effective practice session as well as open your session up to many different types of drills.

Tee
A batting tee is often an overlooked piece of equipment but still needs to be a part of your training regimen.  There are, of course, many varieties of tees on the market today.  Some contain one single post or stem while others enable you to move the post around the area of the plate to work inside or outside pitches.  The ability to move the post is not essential for effective hitting practice.  You can simply move the tee itself around home plate to get the same effect and is really more cost effective.   No matter which type of tee you choose, be sure to work it in to your practice as it is still the best piece of equipment for instantaneous feedback on mechanics and the development of repetition.

Pitching machine
Of all the pieces of equipment listed above, this is the one piece that you could really live without if need be.  Pitching machines come in a couple of various types including wheel based and “arm” based.  Wheel based machines use a rotating wheel to throw the pitch while an arm type machine will catapult the ball towards the hitter.  It really comes down to preference and budget as to selecting the best type of machine.  A pitching machine is non-essential but there is also a lot to be said for predictability and consistency of pitches in practice time for developing young players while more experienced hitters can benefit from hitting high velocity and trick pitches.

Related posts:

1. Hitting Drills – Get The Most Out of Your Batting Cage
2. Hone Your Baseball Skills with Home Batting Cage Ideas
3. Batting Cages – An Overview