Just some thoughts here. I would go to a lumber yard if you can and not to home depot. You are going to pay more money at home depot and get a lower quality product. I would go with 3/4" oak or cherry if you want to stain finish or 3/4" poplar if you want to paint but stay away form particle board as the weight will warp it. Also if you are using solid wood construction you don't reinforcements under boards that are less that 4' long (unless you got down to 1/2" which won't look right). Anyway those number are for games not heavier stuff so don't put studs 4' apart in you floor and blame me, those numbers are specifically for game shelving.
For those of you who don't read long messages....
3/4" Oak or Cherry for stain (match your house if you can)
3/4" Poplar for paint