Kobolds: They used to be described as "dog faced" but looking at their old 2e picture in the monstrous compendium
http://cite.blanche.free.fr/cite/Creatures/KOBOLD.JPG I can't for the life of me figure out what dog they were supposed to look like. They were pictured as squat, rotund, stubby-fingered, flat faced, with big round bug eyes and voices that sound like "yapping dogs". Because they had less than 1 HD, PCs could attack, and slay with a single strike, as many kobolds as they had levels.
Then came the publishing of the 2e colour monstrous compendium book with artwork by DiTerlizzi IIRC. Suddenly kobolds did have their dog-like snouts, were lithe and just seemed like tricky little SOBs. The publishing of the Dragon Mountain boxed showed them in all their glory on their home turf, with multiple tribes with devious traps and clever strategies to twart even high-level PCs.
Third edition continued this upward progression; their artwork improved even more and they suddenly gained a proud heritage as the distant descendants of mighty dragons and capable sorcerors in their own right. Now kobolds can hold their heads high (or as high as they can get them) and be proud of themselves. Check it out:
http://www.wizards.com/dnd/images/MM35_gallery/MM35_PG161b.jpg
ALL HAIL THE MIGHTY KOBOLD!