Due to their small size, there are not many miniatures of normal snakes. The most accurate sized snakes come from HO scale train accessory sets. The first two small snakes are from the Busch Dandelions set (HO1220), while the larger constrictor is from the Preiser Showmen set (16342). For metal miniatures, there are two snakes from the Citadel C29 Creepy Crawlies series.
The HO scale snakes are just the right size, but they are pretty much devoid of detail. The Citadel snakes on the other hand, are slightly large, but I don't think they look too horribly out of scale.
Giant snakes are plentiful in the world of fantasy miniatures. The first are a pair of snakes from Grenadier – the Giant Snake from the Denizens of the Swamp boxed set (AD&D 2010), and the Sludge Serpent from the Horrors of the Marsh boxed set (Dragon Lords 2010). I've also included the Citadel C29 cobra again for a profile shot.
Next are a pair of giant snakes from the Mage Knight CMG – the Snake (Conquest #CM03), and Whisper (Conquest #CM04) originally had lizardman riders, but I removed them from the saddles.
Finally, there is the Iron Cobra from the Fiend Folio. It is described as being the creation of a great magic-user or minor deity, but despite being AC 0 and reasonably resistant to spells, it does not present much of a threat to even a party of 1st level adventurers.
There are two miniatures of the Iron Cobra that I am aware of. One is from the D&D CMG (which I don't own), while the other one is the Reaper Iron Cobra (Dark Heaven Legends 03655) shown below along with the Citadel cobra.
The Iron Cobra is supposed to be 3' long (even smaller than the Citadel cobra), but the miniatures that represent it are all much larger in size even compared to 28mm figures. I wonder if this isn't because people based the size of the Iron Cobra by this picture instead of actually reading the text.
I prefer the larger size, and it is easy enough to re-stat the monster to reflect this change. In any event, since it is an artificial construct, I don't see any reason why there can't be different types produced according to how the creator wants to use them. Small versions could be used for tracking and assassination, while large versions could be used as guardians.
This is nowhere more apparent than in real-life, where mechanical snakes have become a reality thanks to the marvels of modern science. Small mechanical snakes are designed for use in search and rescue operations, while larger mechanical snakes...