If you want a dungeon to be more than a door-busting slaughter-fest you have to add a little character to your dungeons. Monsters need personalities and relationships and there needs to be a reason and means someone may discover these choice little factoids.
Name some of those monsters (no all of them, that's crazy) but for every important looking critter give it a name and for every group pepper them with a few names and personality traits. If you want the player to sneak around the dungeon and find it interesting you have to give them more then a headcount and room dimensions starting with a few odd-balls and stand-out monsters is going to help. If player infiltrate or interrogate those names are going to become very handy.
Names alone aren't going to cut it all by themselves of course along with a name and possibly personality tick some of those named monsters are going to need a hook or gimmick. This can be little things like Gablgoot the goblin tends to fall asleep when on sentry duty, or the Old Red Jhym the turnkey has a few extra keys on his keyring rumored to go to certain treasure chests, Spalreck the Kobold is known to go share lunch with that dragon on level 6. Such little gimmicks are going to add a lot to the character of a dungeon and give more for the players to remember over that 6th room with 7 orcs guarding 200 g.p. in a treasure chest.
There are plenty of name generators and list out there go use the web and find a few. Baby names and names by country lists work well also. Yuo can also use one of those online translators to mix and match words from other languages to add a little accent (he he sorry for the pun).
Two good sources for what some of these named monsters could be up to in this monster business file from Sham, and here at Elfmaids and Octopi at this post, and this one.
You don't need monster NPC with long boring histories you may never actually use a name and a little bit of monkey shines is all you really need to give your dungoens a little more character.