Well, which is it, near term or to sit on for 5-6 years?
If you're looking for more immediate impact, look for players with a relatively clear path to the majors. The Yankees, for example, have all those expiring contacts and a nice crop of young OF, like Austin and Heathcott.
If you're wanting cheap long term upside, look for guys that maybe have an injury history or some blemish on their résumé, but have the potential to be fantasy superstars if things break right. The player that immediately comes to mind is Josh Bell.