One idea I've pondered is the whole OD&D as a toolbox idea always being tossed around. Let's take that a bit more literally as we look at aspects of the rules. In this case, the monster listings. What if they were, let us reasonably suppose, merely to stimulate a budding referee's imagination with regard to his own (ahem) fiend folio?
Which brings us to the mook. You know, the storm troopers from Star Wars, goblins from Lord of the Rings, red shirts in Star Trek, anyone serving with or fighting against Arnold Schwarzenegger in pretty much any film he's been in, etc. They are the ones that need to be mowed down to (a) show how tough our hero is, and (b) to get to the Boss Monster.
Mooks are fun. They give your 5th level players a chance to realize how tough they've become. A lone mook with a single hit die at first level is a credible threat, a group of 4 or 5 at fifth level is barely a challenge. Sure, they can be annoying. They siphon off hit points, cause the party to expend valuable resources such as arrows, healing spells, offensive magic; but it's cool to mow down hordes of bad guys!
Here is a proposal for non-goblin mooks. Nothing wrong with the goblinoid races but it's nice to have something different in your campaign.
RatlingsSimply put, voracious and proliferate anthropomorphic rats. These can range from ½ HD to 1+1 or even higher per the needs of your milieu. Armor class is 6 for mundane types, with natural DAC[AAC] improving for leader types. These leader types may also be in armor, especially if they can get their hands on especially ornate/shiny armor or magical armor.
Ratlings breed everywhere but tend to be found in places man-types typically avoid: sewers, deserted houses, garbage heaps, midden heaps; not because they necessarily like these places but because they are typically undisturbed while nesting there. This is not to say they are not encountered in the wild, there are also wildling and barbaric tribes of ratlings extant.
Ratlings are dangerous for many of the same reasons mundane rats are a threat. They carry disease, create conditions where disease can thrive, and consume or contaminate food intended for human consumption no matter how securely it is stored. Ratlings are also dangerous for reasons mundane rats or not, they are intelligent, vicious, chaotic, and when their hoards reach a certain number of members they become extremely war-like. Thus it always in the best interests of humans and other man-types to deal with ratling infestations before they can become too well established.
Ratling tribes typically consist of a horde of mooks with several lieutenants, the leader's personal troops, and the leader himself. Armor class and hit points/hit dice increase as one goes up the chain of command. The leader himself can be a typically large ratling specimen, or a stronger monster of some type who has assumed rulership of the tribe. The tribe will also have a selection of rules-standard fighters and thieves, as well as shaman and witch doctors; these are typically few in number.
Ratlings have a weakness for hording shiny things. Treasure will tend to consist of coins, gems and jewelry, as well as magical weapons and armor (notable in most campaigns for being ornate and shiny). Less common are miscellaneous magic items or magic-user specific items, though these may be present on a random basis.
There you have it. An enterprising referee could really develop this concept to include all rodentia in his campaign. Thus there might be ruling class of hamster-like humanoids, with exploring otters, fighting mongooses, scout field mice, etc. Have fun!
Note: after coming up with this concept I did a Google search and found out it was not so original as I thought. No matter, my campaign (as are most I've played in) is a pastiche and I've no issue with the idea being possibly influenced by other works I'm familiar with or have at least been exposed to. I just thought I would say this upfront to avoid any "HA HA! Got you! You stole this idea!" type of replies in the comments.