Here is a partial list of my favorite DON augs:
Burnished Turqoise: +10 to all stats, 115 crystals , lvl 48
Thric warded malchite +10 to all stats, 90 crystals, lvl 53
Volocanic Moonstone: +12 to all stats, 90 crystals, lvl 53
Burnished Moonstone: +14 to all stats, 120 crystals, lvl 58
Warded dragon egg: +8 to all resists, 115 crystals, lvl 48
Warded ropse stone: +12 to all ersist, 120 crystals, lvl 58
Frozen Malachite: 100 cold damage weapon proc, 180 crystals, lvl 60
Fire phosphorus: 100 fire damage weapon proc, 180 crystals, lvl 60
Firecore Georde: 175 fire damage weapon proc, 285 crystals, lvl 65
Frozen sky stone: 175 cold damage weapon proc, 285 crystals, lvl 65
I don't have the names of other stones handy as I write this but :
There are stones that increase spell effects, ei: increase damage, range and healing, damage shields.
There are stones that give bonuses to haste, attack, spell shielding, regeneration.
So, Yes getting the crystals is very worth it in my opionion.
Also of note, the items can be returned to the DON vender and traded for about 80% of the crystal cost. Handy for when the time comes to upgrade.
There are two DON merchants one for evil and one for good aligned toons, make sure you get the right crystals radiant (good) or ebon (evil). All the items on both have the same effects, however some of the names are different.
Complete lists of items and augs can be found using the search item features at ally's.