According to the official website, the second movie of "Tengen Toppa Gurren Lagann" titled "Tengen Toppa Gurren Lagann Movie Lagann-hen" will be shown in the theaters in the Golden Week of 2009. Golden Week is a Japanese holiday week and usually spans from April 29th to May 5th.

The movie of "Eureka Seven" called "Eureka Seven: Pocket ga Niji de Ippai" will also be premiered in the same week.

Source: Gurren Lagan Official Website
Source: Eureka Seven Movie official Website

The re-filming of the first movie for the DVD release has already been started and about 100 scenes will be re-drawn. But it will take long before the DVD is available in the stores.

Source: Gainax official blog

Edited on Dec 30th===============
The premiere date of Gurren Lagan Movie was announced to be April 25th, 2009.

Source: Official Website