I love all the lists... it's interesting to read. So I'll offer mine.
All my life, I've been a smart a$$ who likes to break the rules, so no reason to stop now

! And after all, the whole reason we're here is to discuss things
to death, right?

Soooo..... I created two lists, one for the characters I'd have liked to have seen come back, and one for the guest stars I thought had the best acting chops (see, I stayed within the thread topic

).
Best characters:
1. Holly Valance - Lola = "Remember darling, half the world is night." I think she could have been Josef's Coraline
2. Jason Butler Harner - Lance = "Welcome to the family <sneer>."
3. Jacob Vargas - Guillermo = "Yeah, 'cause I work for you!"
4. Nate Mooney - Ryder England = "She requires references - you know that?"
5. David Blue - Logan Griffen = "Can my code name be Lando Calrisian?"
6. Molly Culver - The Cleaner - "Mr. Sloppy and Mr. Stupid got carried away..." I too liked the original cleaner the best.
Best guest stars:
1. Gideon Emery - Donovan Shepherd = "Come on, 2 vamps, 2 lovely ladies... in my day, we called that a party."
2. Mark Totty - Jerry Drake = "Mr. St. John, my time is money. I know a lot of people say that, but I actually had my accountants run the numbers." and "Your movie's gonna rock!"
3. Vanessa Lengies - Leni Hayes = "Who wants to go clubbing?"
4. David Fabrizio - Lee Jay Spalding = "I know what you are, Mick."
5. Hal Williams - Det. Bobby Desmond = "Hey, what's with these muscles? How're you stayin' so fit? "
6. Bryn/Amayla Early - Young Beth = Best non-speaking part

, because those woeful eyes are really heartbreaking.
I'm sure it's not lost on anyone that there's a lot of snarky aspects to these lists
ETA: to clarify... and to add #6 to my first list (one of these days I'll learn to count
)