I graduated with a B.S in Information Science. As I went through university, I realized that I was interested in HCI and usability. However, I did not have much material that would be relevant to building a portfolio to demonstrate UX work. I feel that my current one (www.ctrlaltm.com) is quite bare to be frank and I want to redesign it to make it more appealing to myself and to anyone who views it. I have participated in an open-source project but I did not have much experience in UX at the time so I felt that I was not able to contribute as well as I could have. So I'm thinking of making mockups to put on the redesign of my site.
Anything that could represent your knowledge in Information Architecture and User Experience is perfectly valid portfolio material. It doesn't really matter what's in the portfolio as long as the consumer of the content understand how great you are, and why it would be a loss NOT to hire you. So, yes, Wireframes, Mockups, Use cases, Requirement analysis, Personas and everything else which is the outcome of what we do is perfect for a portfolio.
Mockups, etc. are fine. In fact they're good.
When I look at a portfolio I'm looking to understand how a person works - now what the final results look like. The final results are - in any non-trivial project - down to many people. I need to understand how the person helped do that. Mocks, wireframes, pencil sketches, etc. are all good.
One thing though. Be very clear what the status of the work is.
Having mocks and sketches from student projects or personal work is completely fine. Making student or personal work look like client work will get you binned. Since we'll ask about the clients in any interview you get ;-)
One of the things I would like to add to Bennys answer is to "show your work". Often UX architects or UI Designers will show the nice pretty completed work. That's ok but the person hiring you wants to know how you got to the end work. Most of my portfolio is of hand sketched wire frames, thought concepts, information architecture etc. Just showing the pretty stuff doesnt cut it anymore.
I use anything and everything I can think of in my portfolio -- and in fact, I've been dinged by other folks for NOT having mockups and not "showing enough of my work", because it's that showing of your work that separates you from a mere web designer and makes it clear you actually know what you're taking about.
They want to see a lot of things, but because a UX Designer works as part of a team communicating with other folks and justifying your choices in a corporate setting, you should show them your process, which includes:
- Rationale for doing things one way vs. another
- Findings and evaluations of previously / currently existing systems (e.g. fantasy redesigns of Amazon or another site)
- Mental Models
This said, make it clear what you did, who you did it for, and when you were working for someone else / a class vs. your own fooling around. Having a project that your professor eventually pulled the plug on is fine. It doesn't have to be complete, it doesn't have to have made it into production, but you do need to be honest about it.