The wikipedia article on Let’s Play videos lacks an example. This is understandable. Wikipedia isn’t video heavy and the vast majority of games are locked down under extensive copyright.
There are some free ones though. The one I’m most familiar with is Battle of Wesnoth. A pretty solid game and a search of youtube shows that let’s play videos of it do exist. However such videos are pretty long. There isn’t much work on how long encyclopedic videos should be but I feel for that for the most part they should max out at under 10 minutes.
Probably the best bet in that case is would be racing type games. Looking at wikipedia’s list a couple of them are based off the light cycles from Tron. I’ve actually played one of the (GLtron) and while fun there are potential copyright issues here (although lets face it no one is going to sue). X-Moto looks rather like an elasto mania clone. I’m not aware of much caselaw in the area but it might be a theoretical concern. Speed Dreams looks to be the best option in terms of copyright, graphics and actually being out of alpha/beta. Copyright wise and lets play video of the thing would need to be released under the free art license.