The Mirror have a story that United have made an approach for Arda Turan of Atletico Madrid, but he's more interested in joining Chelsea. Chelsea have a better side and manager than United do, so you can see why he'd prefer a move to London than Manchester. That's if he hasn't already agreed a move to Barcelona anyway. You can read the story here.
In the Guardian, it appears that Robin van Persie has agreed terms with Fenerbahce, and is negotiating his sale from United as he still wants a year's salary. He's on enormous wages at the moment, so you can see why he'll be making sure that his move to Turkey, for £5 million, doesn't cost him. You can read about him here.
In ESPNFC, there's quotes that Sergio Ramos is, 'not negotiating with anyone.' Which is quite true, obviously. His agent will be doing the negotiating, should any have taken place or be taking place. It's a non-denial of any potential transfer to United, but doesn't indicate any movement in the transfer.
The Sunday Times also has an article on Nani, Morgan Schneiderlin and Sergio Ramos, but it's not worth reading, and various emphatically Not Credible papers and sites have linked United with Torino fullback Matteo Darmian - wait to see if a grown up reports the story before getting excited.