If you are doing this with simple PHP and MySQL I would suggest you keep track of popularity. Whether that may be in views, buys, clicks, search, etc. From that you can keep a list of the top popular items as they likely would be far more relevant to all your users.
Normally I would suggest better alternatives that use systems to make contextual recommendations for each individual users, but in some cases that sort of technology may not be easily available. But if you do want that sort of alternative, I would be more than happy to elaborate on that answer as well.
I would suggest against voting though. As it requires to add new functionality that may distract from your main functionality. Unless of course the items themselves don't do anything and there aren't any call to actions like buying, viewing, sharing, etc. The performance metrics that you should associate to each item should be updated regularly to keep the listings fresh. You may not want something that was popular a month ago to still dominate your listings.