Perhaps the best example of a market that approaches perfect competition would be the market for some agricultural commodity, especially in a less-developed economy.
Especially in a less developed economy, there are few barriers to entry into farming and so there can be many small farmers who are able to compete with one another. All a person would have to do to become a farmer would be to get a small piece of land and a few tools. This is slightly different in an advanced economy because a starting farmer would need all sorts of equipment and a lot of land. In such a case, the start up costs would be something of a barrier to easy entrance into the market.
The farmer would be selling a homogeneous product. One farmer's potatoes or wheat would be substantially similar to those of the next farmer. There would be no real way to differentiate between them. In such a case, you would be close to perfect competition.