As of Generation V (Black and White), yes. EVs are now applied to stats after every battle. This means that player-visible stat increases may occur when they are not expected, such as an increase in maximum HP after a battle without leveling up—which I've observed while playing Pokémon Black Version.
In Generations III and IV, EVs are generally applied only on leveling up, and Pokémon do not gain EVs when at level 100 or otherwise from a battle that does not yield experience points, except by stat-boosting items. EVs are applied when the Pokémon is deposited into and withdrawn from the Pokémon Storage System (box) as well, which can be done to force any pending EVs to be applied between level-ups or at level 100.
Since Generation III, every 4 EVs adds one point to a particular stat at level 100. For lower-level Pokémon, this stat gain is prorated based on the Pokémon's current level (for example, a level 50 Pokémon with 120 EVs for HP gains 15 HP from EVs, rather than 30 at level 100). Generations I and II use a system called Stat Exp that differs significantly from the current EV system.
See this Bulbapedia article for more information on effort values.
As of Generation VI (X and Y), all EV changes are applied immediately, regardless of whether they are the result of battle, Super Training or otherwise.