why not
I don't know how many of you guys are really privy to the show, but i just watched every episode straight (don't ask). With SG1 being a 3 person team, it doesn't seem right, as some of you have mentioned earlier. Jonas Quinn would seem the best fit IMO not just because he has been on before, but because it wouldn't be such a shock to the audience as well. He isn't just an egg-head as someone else suggested earlier. He doesn't just sit and think, he has done action scenes as well as diplomatic scenarios. Also,he has some kind of genetic difference between him and other humans since his branch of humanity was isolated for so long - analogous to a kind of an austrailian evolution thing i guess, he has this memory capacity that proved very useful during their season 6 missions, can manage weapons as well as teal'c or sam, and had interesting quirks that helped the character stand out (ex. his obsession with the weather channel). He also brought naqadria to the table and we have yet to see themes of current episodes return to this element (not to mention the tok'ra). If he joined, we wouldn't have to wait through a bunch of episodes for the character to get assimilated into the SGC collective, Jonas already has a place there. If he doesn't join SG1, he should at least show up more, IMO.
Sam = military leader + scientist
Teal'c = warrior and priceless experience with goa'uld technology
Daniel = Anthrop-Archae-ologist and recurring voice or reason
Jonas = already good at playing the new guy as the previously mentioned attributes above.
while these all may seem like weak arguements to bring him back, i would hate to see them bring in some other character that just seemed like a recycled jack o'neill. we already have a jack, lets bring back someone we already like. i don't know the first thing about tv shows or script writing so i don't know how feasable it is, or if corin nemec is even interested. i guess we'll find out