Inside Fights gives a few updates on the UFC 105 card: 

A tipster has informed Inside Fights that Michael Bisping will meet Denis Kang at UFC 105. However, despite recent reports to the contrary, the fight will not serve as the main event of the evening.

...

A source within the UFC has confirmed to Inside Fights that BJ Penn will likely defend his lightweight title against Diego Sanchez in the main event of UFC 105.

The UK's biggest star Michael Bisping will try to bounce back of his knockout loss to Dan Henderson as he takes on Denis Kang. Everyone assumed that Bisping would headline the event against a guy like Wanderlei Silva, but now the plans have changes, and the fans have something even better, as BJ Penn defends his lightweight title against Diego Sanchez.

UFC 105 will be in the UK, a place that BJ Penn claimed he would never return to after his purse got affected by poor PPV buys. Some people think that he accepted the fight because the card will be shown to millions of people for free, making him an even bigger star which would also lead to better buys and bigger paydays in the future.

UPDATE from Fighters Only - the fight has been offered to Diego Sanchez:

A source close to Diego Sanchez has confirmed to Fighters Only that he has been offered a fight with BJ Penn at UFC 105... "The fight has been put on the table," the source said last night. "But nothing has been signed and nothing is confirmed at this stage."

UPDATE 2 - From Michael Bisping:

As reported on many websites, I may possibly be fighting Denis Kang at UFC 105. Normally I wouldn't mention anything on my site until I have confirmed it with the UFC, but as I mentioned its all over the internet.

Denis is a very experienced fighter who has fought, and beat some of thhe top names in the sport... I'm sure it would make for an exiting fight and we can make it a night to remember for the fans in Manchester.

If your reading this Denis, good luck in training and I look forward to meeting you in Manchester.

UPDATE 3 - Dave Meltzer says BJ Penn has accepted the fight:

B.J. Penn has agreed to face Diego Sanchez on 11/14 in Manchester, England for the UFC lightweight title.  This will be on Spike, not PPV.

Rumored UFC 105 card so far:

- BJ Penn vs. Diego Sanchez 

- Michael Bisping vs. Denis Kang

- Dan Hardy vs. Dong Hyun Kim 

- James Wilks vs. Matt Brown 

- Damarques Johnson vs. Peter Sobotta 

- Paul Kelly vs. Dennis Siver 

- Andre Winner vs. Rolando Delgado

- Ross Pearson vs TBA 

- Terry Etim vs TBA