What things should a portfolio have?

I am wanting to start up my own portfolio/design website soon and Have been thinking.

What things do a good portfolio consist of?
I was thinking along the lines of being simple, with a wealth of knowledge easily accessible. Yet a design comfortable enough to portray some of the users skill.

What works best for a portfolio, dark and graphical or light and clean?
I would definitely say that a light and refreshing style of portfolio definitely works best.

Opinions?

Light and clean.....should be the way to go.
Unless you are into animation or something where dark and graphical would do the trick.
Basically the portfolio should show off your skills.
Anything and everything.
Proper categorisation and ease of navigation is a must

The portfolio should consist of the very best examples of your work. If I had previously done 10 websites but only 3 of them were decent then I would only choose to exhibit these in my portfolio.

Case studies are becoming more and more popular these days, include information about the project, aims and objectives, the clients feedback etc. The more information you provide for the potential customer the better.

I would also include links to contact information, free quote and pricing. Make sure the page is functional above all, perhaps link to other pages for your design samples. The worst thing that can possibly happen is showing all your work on one page, the client won't bother waiting for it to load and you will lose a potential customer!

Absolutely what Robson said

the design has to be stimulating enough to make the user want to go to your portfolio. the design is the firsdt impress they have of your work, if it's not impressive, you're taking a gamble on whether they'll check out your portfolio to see if they're all duds (to them if they;re already disatisfied) or they'll just leave.

Light and clean, use white colour background for content.

Have it resemble you, show the visitor the real, creative side of you. That is how I am going about my portfolio. I'm just expressing myself and my creative side. I suggest light colors and a very smooth interface. Try and come up with something unique. If you need some ideas feel free to contact me, i'm always up for helping people out.

the best advice i can give, which someone touched on, is offer your best stuff... it's very easy to assume "let's show them every project!", but that will often work against you when you water things down...

i personally have too many projects on mine, and thats cutting out 75% of what i have done... but being that im web and print, and i do a ton of things inside each area of design, it was somewhat necissary...

if youre starting out however, blow them away with your best stuff...

my other piece of advice, is if you are looking to interview, or wow a client, dont put EVERYTHING on the website... save a few really good samples for in person... often times people "blow their load" on the website, and by the time they have their foot in the door, the client/employer has already seen everything...

Eric