I'll second Malachi Martin -- those were some good shows. I can't imagine how ham-fisted they'd sound 10 years later with Noory at the helm.
There's not a specific guest, but a 'sub-genre' that Art had on somewhat frequently that's been co-opted by the generic lame-brainess of 2012 the last few years...
I can only describe it as 'future America'... one guest was Lori Toye (sp?) that had visions of USA post-earth changes and published her new map of America. One other guy, shit, what was his name... the guy from FLA. Gordon Michael Scallion. Kind of a 21st century Edgar Cayce that was having those near-future earth change visions. Supposedly those visions drain him and cause health issues, similar to Cayce.
There were also similar guests with a definite Catholic/book of revelations bent -- one was Kathleen Keating, she hasn't been on in a few years. She was a little out there (maybe even half-whacked), but her shows were enjoyable. I recall the last time she was on I think she rubbed Georgie the wrong way. She stated something with a very pro-Catholic stance, and George challenged her with his typical wishy-washy generic spirituality stance. He basically told her she was wrong, she stood her ground and she hasn't been on since. It's one of the few times George was very aggressive with a guest that I thought he was wrong, even if i agreed with him.
There's another guy that's a catholic priest, belongs to an order that has been excommunicated from the church by the vatican. Believe the guy received Marian visions. Was only on a few times but was a good guest.
Now that I think about it, there hasn't been any Christian/Fatima/Medjugorje/Lourdes shows on in quite some time. recently a guest mentioned St. John of Patmos and I think Snoory enthused "absolutely, there *are* no coincidences" or another similar inanity.
Ok, I'll quit blabbing after this one -- Peter Davenport. Kinda dry, but the guy always had interesting, honest-to-goodness UFO cases to present with well done eyewitness interviews. C2C needs him back, STAT. I'd take Peter any day over LMH.