Best way to record an interview?

What do you think is the best way to record an interview? It has to be able to record up to 1 hour and 30 minutes. But I don't need video, just sound. How long can an iPhone record for? I have a Nikon camera but it doesn't record for more than like 20 minutes at a time. And if I did use a phone, would the file be too big to get on my computer?

I use my iPod for interview recording. I have it jailbroken to be be able to pull it to my PC.

Any cassette tape recorder will do. Just make sure the tape is long enough, or have two tapes.