I got the 55-gallon drum from behind my work place.

Parts list (all from Lowes)
212957 - Flexible gutter elbow (1)
22690 - 4"x3" white pvc s&d coupling (1)
22481 - 3/4" coupling (1)
22681 - 3 & 1/16" to 4" hose clamp (1)
22682 - 4 & 1/16 to 5" hose clamp (1)
22034 - 3/4" X 3" straight pipe (1)
25010 - 1/2" X 52" plumber's tape (1)
21516 - 3/4" hose bibb spigot (1)
20992 - 3/4" Right elbow joint (hard to find, had to look in 3 different stores)
Total cost at Lowes: $15.99 + tax

I needed screen material for the gutter intake and the best price for that was at Wal-Mart. I lost the receipt, but found some for $4 and some change.

I also needed hole bore bits for my drill. I found a set at Harbor Freight Tools on sale for $5 that worked perfectly.

Built exactly as shown here:
rain barrel video

I used the smaller clamp to clamp the flexible gutter elbow to the rain spout on the house that I cut shorter with a hacksaw. The larger clamp is used to clamp the screen to the 3"X4" coupling that fits into the rain barrel.

I actually built two, but for the second barrel I didn't need the 3"X4" coupling, screening or any more clamps. I just needed a PVC pipe section to connect both rain barrels at the top.

Works great and a solid construction with using the elbow joint and spigot extension from the threaded-cap already screwed into the barrel. You see some rain barrels that simply put the spigot directly through the side of the plastic barrel, but over time that is more prone to leaking as the connection is not as tight as going through the cap.

Hope the parts list makes it a little easier for someone else to do the same.