AMC Theatres (and other chains) will be presenting all three films in The Twilight Saga on June 29, starting at 6:30 PM, leading up to the 12:01 AM screening of The Twilight Saga: Eclipse, reuniting the entire cast under the auspices of new director David Slade.
UPDATE: It looks like other theater chains will be doing similar events in case you don't have an AMC near you including Cinemark and possibly Regal as well.
For a single $30 admission ticket, AMC is offering each attendee:
1) Admission to "Twilight"
2) Admission to "The Twilight Saga: New Moon"
3) Admission to "The Twilight Saga: Eclipse"
4) A $10 AMC gift card that you can use at any time (even on concessions)
5) A collectible Twilight lanyard (while supplies last)
For more information on AMC's special fan-friendly event, you can visit the official AMC Entertainment Blog, and for Cinemark, you can get more info here.