These are all of the samples I have gathered that have been used in MMLP2.
Some I have not found yet, but I have found the majority of them.
Rhyme or Reason
This song samples the song 'Time of the Season' by The Zombies pretty extensively, down to its vocal melodies and its entire instrumental.
http://www.youtube.com/watch?v=oc7b62El_fk
Also, at the very end of the track, the words "Who's your daddy" are heard as it echoes until the track ends. This is actually a sample from an earlier Eminem song, 'My Dad's Gone Crazy'.
Berzerk
The song 'The Stroke' by Billy Squire is sampled throughout the song.
http://www.youtube.com/watch?v=bLHc-yIAPbg
There is also a sample near the beginning where Em says "Just like I did with addiction, I'm about to KICK IT!" The words "Kick it" are a sample from the Beastie Boys song 'Fight For Your Right", which Rick Rubin also worked with.
http://www.youtube.com/watch?v=qzD63ys1K8c
Rap God
There is a long string of samples during the intro of the song. These are from audio recordings of the Captain America comic, 'And a Phoenix Shall Arise!'
http://www.youtube.com/watch?v=gERe0pB-DpQ
http://www.youtube.com/watch?v=ODgdBIgM15A
The exact lines that are sampled appear at the 1:07, 5:42, 7:35 mark in the first video.
The exact lines that are sampled appear at the 4:41, 5:18 mark of the second video.
Brainless
The line, "Marshall Mathers, Eminem, the rapper Eminem." from the intro is sample of a scene from the movie Superbad, which is Eminem's favorite movie.
http://www.youtube.com/watch?v=ntTO7HKv4JE
The exact line the is sampled appears at 1:08
The lines ""Who can say for sure? Perhaps a frontal lobotomy would be the answer
If science could operate on this distorted brain and put it to good use
Society will reap a great benefit." that appear in the intro are sampled from an audio recording of a Batman & Robin comic.
Link to the sample: http://www.jeffness.net/blog/Batman.mp3
So Far...
The song 'Life's Been Good' by Joe Walsh is sampled extensively throughout the track, even down to its vocal melody.
http://www.youtube.com/watch?v=063LYBBlR3c
There's also a sample of I'm Back and The Real Slim Shady during one part of the track, but you all know that.
Love Game
The song 'Game of Love' by Wayne Fontana & The Mindbenders is sampled extensively throughout the track.
http://www.youtube.com/watch?v=7RgXQSd9ojA
Evil Twin
During the hook, there is a sample of 'The Reunion' by Bad Meets Evil, which Eminem himself is a part of.
http://www.youtube.com/watch?v=U5AsY3dxXh0
The sample appears at 4:12
Groundhog Day
There are many samples throughout the track, but the only one I have managed to find is the one that goes "I remember it clearly, even today" is from the same recording of the Captain America comic ‘And a Phoenix Shall Arise!’ that was used in Rap God.
http://www.youtube.com/watch?v=ODgdBIgM15A
The sample appears at the 2:12 mark.
.. And that's all I know for now. If anyone knows where the remaining samples come from then feel free to post them here.