The downloadable expansions for Grand Theft Auto IV are now available on PC (via Games for Windows Live) and PlayStation 3 (via PlayStation Store), as promised.
Those with a copy of GTA IV will be able to buy the two--the biker-oriented Lost and Damned and night club-centric Ballad of Gay Tony--at $19.99 each on PlayStation 3 and 1200 Microsoft Points / $15 on PC. As of this writing, both are available through Games for Windows Live, though the PlayStation Store only has The Lost and Damned. Both were released on Xbox 360 across 2009, priced at 1600 MS Points / $20 each.
[Update - 6:00pm CST] The Gay Tony DLC is now on PlayStation 3 as well. [/Update]
Also available is a standalone bundle the includes the two expansions and allows them to be played without a copy of Grand Theft Auto IV. Dubbed "Grand Theft Auto: Episodes from Liberty City," the collection sells for $39.99 on PlayStation 3 and $29.99 on PC, with the latter already available through digital distributors like Steam and Direct2Drive.