The various types of gloves used in mixed martial arts (MMA) are not simply to protect your opponent, they're meant to protect you as well, particularly while training. With regards to the various types of MMA equipment available, the gloves used for training are not necessarily the same as those used for actual combat; likewise, gloves used by professional MMA fighters are different from those used by amateurs.
There are a few different styles of training gloves, and depending on your specific training level and objectives, you may use more than one type. The two main varieties are bag gloves, which are essentially boxing gloves (like a mitten) and grappling gloves, which have separate openings for the fingers and make it possible to use the various wrestling moves permitted under MMA rules.
Bag gloves are good for bag work and sparring, but lack the padding, flexibility and protection of grappling gloves. If you are using bag gloves for training, it's best to use handwraps as well.
Better (and higher-priced) grappling gloves have extra padding over the knuckles, which minimize the risk of serious injury to both combatants. The MMA gloves used by professionals tend to be lighter in weight, topping out at about four ounces. For training and amateur purposes, you will want gloves that weigh at least six ounces, and preferably ten. There are two distinct benefits to wearing weighted training gloves: one of these is of course the added protection in the form of extra padding, but heavier gloves also force you to train harder and aids in the development of the upper arms and shoulders. Aside from the hips, glutes and upper legs, muscles such as the deltoids, traps, lats and triceps are the most likely to suffer strain injuries. Developing extra strength in these muscle groups not only makes you a more formidable fighter, it will help you in avoiding injury as well.
One piece of MMA gear that deserves to be mentioned is the muay thai style specialty fight glove. Like boxing gloves, these are more like mitts, meaning they are no separate finger openings. They are however much heavier than standard bag gloves or grappling gloves; in some cases, muay thai gloves weigh in at as much as sixteen and twenty ounces. There's a reason that many fighters enjoy using gloves and handwraps for training purposes. In addition, muay thai gloves have extended wrist protection, providing support and making it easier for combatants to use the forearms to block punches and kicks.
While it should be pointed out that while many web sites may advertise "cheap gloves," this is one aspect of your gear that you should definitely spend more than a few bucks on. Gloves in the $20 - $40 range are not likely to be very durable or provide the necessary protection. If you are seriously considering taking on the MMA training regimen then you ought to make sure you obtain the proper training equipment regardless of whether or not you are training for combat, physical fitness, or just to learn self defense tactics. Therefore, you should plan on spending between $60 and $100 for a decent set of gloves that will be durable and meet or exceed MMA regulation requirements.