All crystals are useful to meditate with, but these crystals stand out for their versatility and strength.
Black tourmaline is great for its grounding properties and for filling you up with a neutral warm energy.
Black amethyst is a high energy crystal that activates both the root and crown chakra making it very good for getting your kundalini energy flowing as well as working on any chakra or for any healing purpose.
Selenite is a very high energy crystal and is great for when you want a pure energy source to use for general energy work, kundalini work or healing.
Quartz is useful in letting you put energy into it, and then amplifying it back out, as well as being a versatile source of energy to work with.
Rubellite is great at helping your kundalini energy flow by activating both your root and crown chakras, and like black amethyst it also contains some grounding properties too.
In general, crystals that have multiple colors are especially versatile, black and red activate the root chakra while white, clear, and gold activate the crown chakra, combining these colors together gives you a crystal that helps get your energy flowing throughout your entire body.
Black tourmalineand seleniteare must haves, but black amethystand rubellite deserve special attention for their unique combination and strength.