My list an in no particular order (plus only listing character names of they apply)
Neal Patrick Harris: either as a sidekick or villain would love to see him in Macgyver
Hilary Duff: I have a celebrity crush on her have t really seen her in anything but she is so pretty I think she could do the Penny Parker role with ease as Hatcher usually played it campy anyways.
Colbie Smulders: another celebrity crush of mine no idea what she should play maybe Nikki Carpenter but that might seem too similar to her shield and Jack Ryan characters...
Mads Milksen: would love it if he was Dr Zito and if Dr. Zito was the main villain of season 2 (I am thinking a season that is a fictionalized versions of the Zodiac killer event and of course the two epsiodes Zito was in... I just don't want Murdoc introduced too quickly as with Arrow once you throw in your big baddie the fans all know by season 3 where do you really go from there)
Michael Chiklas: I still say I want him as Peter Thorton and I still say he would be amazing
Wesley Snipes: the bounty hunter whose name I can't remember from the Epsiode Ma Dalton.... Jessie Colton I think is the name... Back when we had no cast at all I was thinking him for Thorton but now I don't think I would like that but I think Snipes would be cool in the bounty hunter role and maybe they could play with the character and make him somewhat of an anatomy its for the season before realizing his strings are being manipulated too (maybe in my season 2 zodiac killer idea Zito realizing Macgyver will ruin his fun hires Jessie to deal with him)
Summer Glau: Deborah... Yeah sorry I still want her as the main villain of season 1 (since all we know is it's a girl who once had a romantic intrest in Mac) she is hot sexy can do action sequence can read off the science stuff like she knows what she is talking about and can play the villain quite nicely (as season 2 of arrow and a few epsiodes of the Sarah Connor chronicles proved) I get her as he main villain I would be beyond happy
Timothy Dalton: I believe he hasn't retired yet... While I doubt him of Brosnan would do it would be really cool to have a former 007 playing any role really in Macgyver..
That is about it for now