For nonstop rambling I’ll just let my eyes glaze over and sit in silence. If I’m interrupted while I’m talking I say “But enough about me, let’s talk about you again”.
Another ploy I have seen used to some effect is when the other person is so wrapped up in the sound of her/his voice that she/he isn’t aware of your presence and just keeps prattling on and on, just open your eyes wider and wider as if there’s something coming up behind her/him, or just duck down as if something is about to hit her/him in the back of the head.
Also and big widemouthed yawn can do wonders to interrupt the spiel.
My favorite response of all time was from a CBS news reporter named Michelle Clark. She was interviewing Hubert Humphrey, live, and as was his custom, Humphrey simply would not shut up. With the director franticly signaling her to end the interview NOW, Clark leaned over and, out of range of the camera, grabbed Humphrey’s upper thigh (some accounts say it was a little higher than the upper thigh) and squeezed. He stopped talking and she signed off the interview.
However, like LSLGuy’s suggestion, it may not be appropriate in all situations.
Ya know, I killed a guy in Reno once…just because he would not shut the fuck up. <stone cold stare at offender>
I find that simply turning my head away from them tends to work well enough, though it can take a while for them to peter out.
I believe the modern incarnation of this is the “Cool story bro”.
In order for me to consider someone a friend, we have to be able to be direct with each other. If we were friends, I would say “dude, you have to shut up.” If we’re not friends, I probably would pretend that my iphone had a call coming in.
“We all have something to bring to this conversation, so from now, I think you should bring silence”
(Thought that was Blackadder, but it doesn’t seem to be).
I start re-arranging the silverware drawer.
“As the Good Book says; Shut yo mouth, bitch.”
“We all have something to contribute to this conversation. You, I believe, should contribute silence.”
Um. OK
“That roast should be done by now.” (walk away)
Look them in the eye with a kind expression on my face.
Make a “shh” gesture with my finger to my mouth.
Then insert one of the following:
“You’re talking to much for me to understand what you’re saying.”
OR
“I’m done listening now.”
OR
“I just developed a pounding headache.” <walk away> “Ah…that took care of it.”
OR
“Less talking, more walking.”
OR
<Indian QuikiMart accent from Simpsons> “I cannot believe you will not shut up!”
OR
“This is fun and all, but I got stuff I gotta do.”
OR
<with finger still to lips in “shh” gesture, slowly back away, all the while maintaining eye contact>
i lost the train of thought would you please start over from the beginning. (repeat as necessary)
brevity is the soul of wit.
If I can’t get a word in edgewise, I raise my hand like i’m back in school.
If they still won’t stop, I wave it in front of their face.
One blowhard I know was going on and on and I finally said, “You know … between the two of us, I think we know everything there is to know in the world.”
The guy asked, “Why do you say that?”
To which I replied, “You seem to know everything except for the fact that you are an insufferable bore, and I know that!”
Larf! 
When people start going off about how “they” should fix the economy or deal with the Middle East or anything political, I say “This is all good stuff, you should write a letter to your congressperson.”
That’s flummoxed my parents into shutting up a few times.