If you want to future proof then get a good PSU from reputable brand and plenty of storage as these are most likely what move with you into future builds/upgrades cycle. DDR 3 1333mhz is going to be around for a little while even though trends are pointing to 1600.
Celeron or Athlon AM3 give you room to upgrade. For cases check out gumtree and ebay as you might be able to pick up Lian Li for less than 50 if you like their designs. Same for monitor or see if someone has a spare.