I've invited a lot of guest speakers over the years, but I tried something different recently, inviting a guest speaker who was quite a long ways away to talk to my class via Skype. It worked out really well. I don't think it had as much impact as if he had actually been present, but the fact that the speaker was responsive to student questions and had an interesting presentation overcame that lack of physical presence. In the end the students gave it a big thumbs up. One suggestion I have for doing this (or any other guest speaker) is to have some follow-up on a subsequent week. You can be pretty sure that the speaker will still be thinking about the visit for some time after (in general they love talking to college students and get quite a buzz from the experience), so I have the students make up a series of questions and I email them to the speaker a few days after the event. If the speaker replies (they always do), read/email his responses to the class. They'll appreciate the additional effort.