you are bored? that's the wrong reason to try, you will get hurt, if you summon cuz you've got nothing better to do, whatever you summon will see how unprepared you are, or realize you did it for the wrong reason and attack you.
you can summon anything astral really, dragons, demons, spirits, gargoyles, faeries, whatever. sending them back is another issue, as they might get here, see how powerful you are, and might think to stick around. you might not be able to see them, but they'll make there presence known. it works, and as i said it can be very dangerous. if they're nice, they can help you in your spell casting, or protect you for a short time.