Elladan and Elrohir's role in the story was omitted from Peter Jackson's movie adaptation. However, attempts have been made to identify some of the elves glimpsed during the film with the twins.
At one stage, the elves standing next to Arwen during the Fellowship's departure from Rivendell (Image 1 - FotR extended edition) were thought by some to be candidates for her brothers. The elf on the left has been named on a Decipher card as Golradir. I don't know if the elf on the right has been officially identified (any info appreciated!).
Alternatively, many fans have identified the elven smiths, seen reforging Narsil in RotK, as the twins (Image 2).
For the "book cards" created by Weta Workshop for Decipher's Lord of the Rings trading card game, Rob Gillies was cast as Elladan and Elrohir. (Image 3 - Elladan card, Image 4 - Elrohir card, Image 5 from an article on the Decipher LotR TCG website, and Image 6 from War of the Ring's photo forum.)