there are two things you have to worry about it seems. Not only treating the room with traps for mixing purposes, but it sounds like you also want to treat it for recording vocals into a mic. Realtraps has a portable vocal booth just for this purpose:
http://www.realtraps.com/p_pvb.htm Treating the room is a great thing to do...but you'll still get noises from around the room that you probably don't want recorded (computer, traffic, etc.) This will help isolate you a bit.
Now treating the room for mixing is another thing you want to tackle. Always start with low end treatment...bass traps. You can look at the links above or if you are handy enough, purchase some OC 703/705 in 2" to 4" sizes and place them in your corners (wrapped in fabric). You can either just set them in the corners...or build cool frames for them so they look more a part of the room.
After that, treat your first reflection points. You can still use OC 703 for the first reflection points. Just build a frame for the fiberglass and hang them on the wall.
Here's a big list of distributors of fiberglass:
http://homerecording.com/bbs/showthread.php?t=179563