I'm a huge Hart To Hart fan (it was my all time favorite series till I got readdicted to SMK at the end of January) and they have a lot of repeat sets on there. The ones I remember:
Relative Business - The club they ate at looks the same as a restaurant that appears on at least two Season 2 episodes of Hart To Hart (Operation Murder & Murder Of Jonathan Hart if anyone wants to check). Also the villain's home where they all get captured appeared on Harts Under Glass in Season 3. I recognize the stairs, the hallway coming from the stairs, and I think the room they were held too, but I'm not positive.
Playing Possum - The cafe they go to find Svetlana at was a Parisian sidewalk cafe on the Season 5 episode Hostage Harts.
Always Look A Gift Horse In The Mouth - At the party, there's an exterior shot of Rheza talking to the creep and I think Lee joins them at one point. I'm almost positive that exterior was used on the Season 3 episode Murder Up Their Sleeve.
Affair At Bromfield Hall - Much of the same manor house is used on the Season 5 episode Harts & Hounds. I recognized the front steps, the exterior of the stables, the room with the stairs, that stunning library with the secret door, and I think the ballroom was a dining room on the H2H ep, but it's hard to tell for sure with all the people there.
Also, I think I've seen people comment elsewhere about this, but the Soviet embassy on Bad Timing was the JAG Headquarters on JAG. And Murder She Wrote used it in Season 8 for the outside of the Soviet embassy as well! (Can't recall the ep though, but I couldn't help but wonder if they used the same stock shot from SMK).
I've been watching Charlie's Angels and you see a lot of those panneled station wagons on that show! I also spotted Martha Smith in the opening of the episode "Lady Killer" - she gets killed in the cold open. Ouch! But it's been fun to see the number of huge name guest stars (Sammy Davis, Jr.), in addition to the up-an-coming guest stars (i.e. Kim Basinger). Not to mention watching KJ pretty much solve every case. Sabrina was always my favorite!
And another one... Beverly Garland in an episode of Danger Man (aka Secret Agent in the US) Season One, Episode 27 "Bury the Dead." She looked SO familiar and sounded SO familiar... looked it up on IMDB and, yep, it was our Dotty! And in a show about spies! As an aside, I highly recommend Danger Man, which stars Patrick McGoohan (also famous for the cult classic "The Prisoner"). Lot of fantastic 60s cold war espionage!