However, DS9 didn't get the full Frakes! He left the beard in the bathroom sink for that one. ETA: Of course, this was the finest moment of Frakes' career.
Im going to ignore the Shimmerman's, Alaimo's, Comb's and Robinson's of this world [as we all KNOW they were fantastic] and give a mention to one I have not seen mentioned yet. Jeff McCarthy was great as Roga Danar in the 3rd season TNG episode, "The Hunted".
I think Iggy Pop as Yelgrun the Vorta was a great guest appearance in "The Magnificent Ferengi". "And I thought the Breen were annoying". I think Yelgrun was a great character and put a really interesting spin on the Vorta. Iggy's age and jowels made the character different from the other Vorta we see, which look like teenagers or college kids. Rational, because they're all clones that don't seem to have much of a life span, but Yelgrun's attitude is much different from the other Vorta. He is still a negotiator, but more outwardly aggressive and much more quick to show irritation. I'm not a particular fan of Iggy Pop's music, but I think he's an interesting guy, and it was cool to see him on Trek. Also loved old Koloth, Kor and Kang in "Blood Oath" - all three performances added a lot of depth to the characters.
I'm rather surprised this name hasn't popped up yet: John DeLancie Granted, there were some episodes where Q wasn't all that great, but overall, he was great in the role. Others I liked Stephen Hawking James Sloyan Jeffery Combs JG Hertzler (even in Enterprise and Voyager) Alfre Woodard Whoopi Goldberg
...or, if a car can be a character, how, about the '65 Corvette Stingray in the opening of "Star Trek?"...in reference to the "Kill the Main Character" thread, guess they killed that one off...
Not going to repeat any already mentioned, eg, William Windom would be very high on my list if I'd posted earlier: Morgan Woodward (Simon Van Gelder, TOS, Dagger of the Mind; Captain Tracy, TOS, The Omega Glory) Ted Cassidy (Ruk, TOS, What Are Little Girls Made of?) David Opatoshu (Anan 7, TOS, A Taste of Armageddon) Jeff Corey (Plasus, TOS, The Cloud Minders) Mark Harelik (Kashyk, Voyager, Counterpoint) and of course: Roger C. Carmel (Harcourt Fentin Mudd, TOS, Mudd's Women, I, Mudd)
Her Wow, can't believe no one has mentioned Fionnula Flanagan, she always raises the quality of a TV Show episode Ambassador V'Lar on Enterprise Doctor Tainer in TNG Enina Tandro in DS9 And of course the usual, Ronny Cox, Jeff Combs, JG Hertzler, Louise Fletcher
^ Great call on Sloan/Sadler, in my opinion definitely a character that was played very well with relatively little screen time. The one episode where we get inside his head, believe it's Extreme Measures, gave him as much depth as any regular character. We could devote a whole other thread to the similarities between Garak and Sloan, although they are both clearly separate and equally well-played characters.
Michelle Forbes, without a doubt. Everything a woman should be - intelligent, strong, devistatingly beautiful. She's kind of aged more than one would've expected from someone in Hollywood, but ... when her rose was in bloom, she was quite exceptional. She's still got a lot of talent - she's as sharp as a diamond!
I think Martin Sheen would have been great in that role, and would likely sing his praises just as loudly. Might have to look up that anecdote later tonight, my guess is that he probably just wanted a little too much money and that's why we got blessed with Sadler.