I'd go for Vivaldi's 'The Four Seasons' which has the added advantage of being recognisable, even to people who know little about classical music - like me! You could also check out Paganini, a musician blessed with very large hands who exercised his ego by composing violin pieces so fast and complex that only he could play them, a sort of Jimmy Page of the violin!
The 3rd Movement (Storm) from Summer of Vivaldi's Four Seasons.
Also, Winter, and Vivaldi's Concerto for 2 Violins.
Bach's Prelude (I forget the details)
Ignore the above! The fastest classical violin piece by a MILE is 'Flight of the Bumble Bee' by Rimsky-Korsakov. Some of Paganninis stuff is much faster than any of the above too.