According to E!'s Watch With Kristin, Jeremy Davies is joining the upcoming season of Lost. She also names Rebecca Mader as someone else that has joined the cast.

Kristin writes:

We're hearing that creepmaster Jeremy Davies (Saving Private Ryan) is doing eight eps of of Lost this season, and one Rebecca Mader will have a major recurring role as well...perhaps as the much discussed Charlotte?

It seems that, according to TV Guide, Lance Reddick has also signed on to star in the series.

They write:

Sources confirm that The Wire's Lance Reddick has been cast in the recurring role of Arthur Stevens, the intimidating corporate-recruiter character I first told you about in last week's Ask Ausiello. Reddick also had a lengthy arc on HBO's Oz, where he starred opposite returning Lostie Harold Perrineau.

Dont't forget to also check out: Lost