If you're just tuning in to the Fringe, I can make no better recommendation for this weekend than to buy a six-show pass (for the price of five tickets) and go see some of the Critic's Picks that CityBeat writers have identified (head here to read through all the reviews).—-
My personal Fringe choices are Harold, The Finkles' Theater Show, Tantric Acting at the Holiday Inn, A Brief Lecture of Another Time and Blue Collar Diaries. If you want something a bit more traditional (although still Fringe-worthy), check out Cyrano or Trust; the former is a production featuring the Cincinnati Playhouse's interns, while the latter is the company of interns from Ensemble Theatre of Cincinnati.
And if you're seeing shows on Saturday, be sure to stop by Know Theatre later that evening for the closing night celebration. It's always a blast!