I typically try to grab rookies of my favorite players. I like building sets as well which usually falls in the mid grade range overall.
Speaking of rookie cards..Did anyone see the 57 Unitas go for 25k recently. I thought it pretty amazing..or I'm ignorant of pricing of higher grade cards as I skim past them out of my price range.. .on eBay
http://www.ebay.com/itm/351758389555