Everybody's PLC is different from everybody else's. If you have a particular brand of PLC where you work and you want to get good with it, stick with that PLC's vendor supplied stuff ($$$$$$$). You may find some real good software deals on eBay but beware of pirated copies. I can name 2 electricians that sold bootleg Allen Bradley software on eBay and got severely blistered for it when A-B caught them.
What has always worked best for my guys was a shop built trainer that could be used for learning/immagineering.