The idea of lizardmen always struck me as one of the cooler "mash up a human with an animal" type of monsters, because they're a bit squick-ish. The first picture of a lizardman in Greyhawk (which I use primarily for monsters and the paladin class), after all, was sufficiently cool to be TSR's logo for several years. And it has always struck me as a neat D&D monster just begging for variants, but apparently even modern editions haven't done too much of interest with them.
So, I spent an afternoon a few weeks ago looking up different facts and ideas about different types of lizards. And, as is my wont, I translated some of these things into game-ready ideas: nothing really too extreme, but enough to make a class of monsters varied and fresh for a number of encounters.
The race of lizardmen results from a long-ago magical cross of humans with various sorts of lizards. The "standard" lizardman type is in fact a mongrel of different breeds, which has few if any of their special qualities. Purebred lizardmen have preserved their characteristics much more strongly, and are named for their lizard progenitors. All of the lizardmen types noted below regenerate at a rate of 1 point per turn.
Iguana - These lizardmen have a third eye, which allows them to see through magical invisibility. 25% of the time they will be accompanied by a shaman who is effectively a 2nd level magic-user.
Chameleon - Like their namesakes, these types can change their skin color to match their surroundings. Groups encountering chameleon lizardmen are surprised on 3 in 6 instead of 2 in 6. Chameleon lizardmen are usually found in small hunting packs.
Komodo - Based on komodo dragons, these lizardmen are considerably larger than average and have armor class 4 and 4 hit dice. Their bite (used on 1-2 in d6) is a powerful poison, which acts as a slow-acting poison described elsewhere in this book*. Fortunately, Komodo lizardmen are almost always solitary creatures.
Plated - These massive lizardmen have heavy plate-like scales, and correspondingly AC 3, but only move at a rate of 3". They do an additional 2 points of damage based on size.
Horned - Although they more resemble frog-men covered with short, pointed spikes, the defining characteristic of horned lizardmen is their ability to squirt a stream of blood from near their eyes. This is not poisonous or caustic but, if the target fails to make a save versus dragon breath, he is blinded for 1d6 rounds.
Spiny - These lizardmen are light, fast (base move of 9"), and walk effortlessly on walls, being closer to lizards in their stature. Their bodies are distinguished by short spines that resemble those of Horned lizardmen.
* My poison rules are actually somewhat more forgiving than the standard. Slow acting poisons work as follows: if the saving throw is failed, they do one die of damage per turn for 6 turns. At the end of the 6 turns, if the character is still alive and has not been cured, he (or she) makes another saving throw; this one is "save or die." You're free to make komodo lizardmen have save or die poison if that's how you roll.