The first DLC is set to be released on February 1st, 2011, the catch is Microsoft struck a deal to have release come to the 360 first, so the PC/PS3 release dates are some time after that.

All that is known so far is that the DLC will consists of 5 maps, 4 mulitplayer maps with 2 of them being set in locations played in the single player campaign and the other 2 will be set somewhere during the Cold War time line. The 5th map will be for zombie mode.

No clue if it will cost money on PC, but the DLC is set at 15$ for the 360.

http://kotaku.com/5715089/black-ops-first-downloadable-content-is-oscar-mike?skyline=true&s=i

It probably will. My guess is they will follow the formula of MW2 to the letter.  Which means that we should expect another map pack some time in mid June as well...

My guess is the first will be $15 and the second will be $10 for pc.

I second that! There's no reason why they wouldn't miss an opportunity to milk us die-hards for more money....sigh...