I use THIS
for my own portfolio. I have the 22" x 17" and each piece is mounted on a high-grade black art paper. It's easy to flip through, easy to carry, and keeps forever. For items larger than that I have taken photos and mounted those.
I've interviewed dozens of graphic designers over the past 2 years and i've made a few notes about their portfolios and my own preferences:
1) The large-scale portfolios matted on artboard look nice only if they are done perfectly and consistently from one to the other. Any difference, no matter how minute, becomes blatantly obvious when you put two pieces side by side.
2) The smaller portfolios (linked above) are easy to turn through, are easy to maintain and don't require a large table to view them on.
Now, having said all that, if you're going to be showing these to clients you may wish to go with the larger-scale presentation. Lightwizard's suggestion of the CD/DVD Roms is a good one, as it leaves the client with something to go back to if they wish to.
As an addition to what LW said in regard to the matted prints, I would also consider covering each print with a layer of tissue paper, attached to the back using glue or art tape. This gives each piece a more professional feel.