According to product listings on Amazon's UK site, Fallout 3's "The Pitt" and "Operation Anchorage" will soon be packaged together and sold at retail.

The packs will be available for both 360 and PC, and are currently slated to appear in late May. You will of course require a copy of Fallout 3 to be able to play these expansions.

No official US pricing as of yet, but the bundle will be 15 quid in the UK (which is USD$22).

[Amazon]