Wizard of the Coast released several sets of plastic miniatures for their skirmish game (the collectible card game idea translated into miniatures) and continue to do so in support of the 4th edition of Dungeons & Dragons. We played the skirmish game a little bit, but mostly we used the miniatures to liven up our roleplaying games without the fuss of painting a ton of figures or relying on substitutes. I found most of my collection rather cheap on ebay because the grunts and minion monsters typically were not in demand by the collectible miniature buyers.
I think Wizards hit their heyday in plastic minis with the Underdark set (released in late 2005). Not only did the theme have a lot of cool figures, but the production values were fairly high and consistent. After Underdark, the overall quality of the castings and paint jobs declined; they were not as poor as the original sets, but they were bad, if in different ways. Pictured at the right is Underdark's Half-Fiend Ogre. I like this guy because he could simply pass for any kind of fiend and he looks great.