Note: this bed worked so well I made two more, this time supported with a combination bookshelf/ladder.
Step 1: Materials
Four 2" x 4" x 8' construction lumber
Two 4" x 3/4" x 10' finished knotty pine
One 6" x 3/4" x 10' finished knotty pine
One 8" x 3/4" x 10' finished knotty pine
Two 8' x 4' sheets of just about anything - plywood, mdf, particle board, whatever - the mattress sits on it so it could also be slats if you like. I used 1/2" plywood, because I had a project in mind for the offcuts.
3" deck screws
1 1/2" drywall screws
Eight 6" long 1/4" lag screws with washers
Ten 3" 1/4" bolts with nuts and washers
Two 6" 1/4" bolts with nuts and washers
You should be able to pick this up for about $150, less if you have some materials lying around.
Step 2: Tools
Saw (I used a mitre saw and a table saw during this build, but a circular saw or a even a hand saw would be fine)
A router is good for rounding edges, but sandpaper and elbow grease works too.
A studfinder is useful, or you can use Eric's magnet trick.