I've been keeping this list on another site and felt I should share here as well. There's are all things I've been able to confirm that there has been contact between the Bengals and the following players. If you guys have any sources or info on other prospects feel free to comment (with some source) and I'll add it to the list.

Combine Interviews:

Brandon Saine RB OSU (Not 'official')
Taiwan Jones RB EWU
Will Rackley OG Lehigh

Private workouts/Visits:

Cam Newton QB Auburn
Nathan Enderle QB Idaho
Danny Watkins OG Baylor (already happened)
Andy Dalton QB TCU
Colin Kaepernick QB Nevada
Patrick Peterson DB LSU
Da'Quan Bowers DE Clemson
Greg Jones ILB Mich St.
Rajric Coleman S Utah State
Ryan Mallett QB Arkansas
Evan Royster RB Penn St.
Torrey Smith WR Maryland
Vidal Hazelton WR Cincinnati* 
Buster Skrine CB Tenn. Chatt
Vincent Brown WR SDSU
Nick Fairley DT Auburn
Chris Conte FS Cal
*Does not count against the 30 visits/workouts allowed.

Pro Day Visits:

Von Miller. (TX AM) Visited - Zimmer
Auburn Visited - Defensive Coaching staff and Marvin (Heard contradicting reports that Gruden was/wasn't there)

Alabama - 'Scouts'
Andrew Jackson OG (fresno St.) worked him out one on one. - 'Scouts'
Clemson - 'Scouts'
Andy Dalton TCU - Gruden
Prince Amukamura Neb - Coyle (DB coach)
Derrick Locke & Randal Cobb UK - Anderson
Derek Sherrod Miss St. - "Asst Coaches"
Nathan Enderle Idaho - Zampese
Ryan Mallett - Zampese
Patrick Peterson - ' Scouts'
Pat Devlin - Zampese
Pittsburgh Sheard and Baldwin - Hayes and Gruden
Christian Ponder FSU - Lewis & Gruden
(Wilson/Leshoure/Liuget/OL) Illinois - 'Representatives '
(Scott/ Smith) Maryland - 'Representatives'
Blaine Gabbert Missouri  - Lewis, Gruden & Tobin
Temple  Pro day- Scouts. 
Lehigh (Will RackleyOG) - Alexander
Evans/Williams Virginia Tech  - Anderson
Buster Skrine Tenn Chatt- Scouts
Delone Carter  Syracuse - Anderson
AJ Green Georgia- 
Kaepernick QB Nebada  - Zampese

Link to the Senior Bowl roster: http://www.seniorbowl.com/northroster.asp
Remember the offense was under Brat at this time, so Gruden and Urban were not with the team yet, so Wr's and QB's these two may want to revisit. While OL and RB's most likely have a good grasp on the players already.
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Keep a look out for more updates.
* = Rumored but unconfirmed