Off all the methods I've seen, the IKEA shadow frames are my favorite for mainly display purposes.
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I went a bit different route as I "play" with my minifigures frequently and need easy access to them. Any shadow frame or display case with opening fronts were too expensive for me. Here's the 2 approaches I took. One for display and easy access. The other for storage and easy access.
Display ($10 display case + ~$10 of LEGO parts which is optional)
http://statigr.am/p/186455291754263438_48890075
$10 plastic display case from Container Store (available online too).
The container is almost exactly 30x15 studs in dimensions.
The levels are adjustable. I configured it to have 3 levels and added some plates and bricks to make each level have 2 levels to give a 6 staggered level look. I don't recall the pricing, but LEGO pieces probably cost around $10 as I have access to LEGO pick-a-brick for the 2x4 bricks.
Display cases are stackable. If anyone is interested, let me know and I can take a better and more recent photo. Not as convenient as a display case with opening front, but not too bad for access.
Storage ($5 baseplate + ~$5 plastic container)
http://statigr.am/p/192614052952879352_48890075
$5 baseplate
~$5 plastic container. Container is from Walmart. Plate just fits in the width, but container is rectangular so extra space for storing other things if you want. Lid is loose and completely removable and locks in place by 2 latches.
Containers stack very nicely.
If you really want to pack them in, you can remove the accessories from the hands and move most of the minifigs so they are only 1 stud apart. As my collection grows, I plan on doing that. Also, for rarely used minifigs I will probably put them in plastic bags and just pile them in a container.
Let me know if anyone is interested in better and alternative views. Those photos are old Instagram photos I took a year ago when I was getting back into LEGO from dark ages.