When you say "block", do you mean absorb? Are you looking for do it yourself treatments of ready made?
If DIY, fiberglass is the most commonly used item for absorbtion. Owens Corning 703 or 705 series panels are popular for removable panels. Linacoustic RC is popular for permanently adhering to the wall and then covering with fabric. IMHO, most any brand of fiberglass would work, and is certainly going to be better than bare walls.
In order to trap the bass frequencies, more fiberglass is needed. (either more dense, thicker or more in qty). Some people simply buy the roles of insulation found at your local building store and place them in the corners. You can also use the OC 705 I mentioned above and straddle the corners with that. You could also construct columns from wood and chicken wire, then fill the cavity with fiberglass insulation and then cover with fabric.
Try the search function in this forum as there are lots of links and info available.
I suggest looking at a BFD for bass frequencies. If you don't know about it, the BFD is a parametric equalizer and costs about $120 at any local music supply store like Guitar Center.