Tour de Suisse, Paris-Nice, Dauphiné, País Vasco and Tirreno-Adriatico, but it does shift around. At the moment the Dauphiné is decreasing a bit in prestige as it's being treated as more of a training session with UCI points than a race in its own right since ASO took over, although this year's parcours is a positive step against that. Tirreno is increasing in prestige, however, as a few years ago it was nothing more than a preparation race that could be won by a sprinter or was just won in the time trial, and has developed into a race with characteristics all its own now.
Dauphiné and Suisse are big races because they have the characteristics of Grand Tours in shorter races (big mountain passes, long time trials, transitional stages); Paris-Nice is the opening curtain for the stage racing calendar and has increased status due to that, a bit like Omloop for Classics season; Tirreno-Adriatico and País Vasco are very difficult and comparatively unique stage races with strong support which makes them into a big deal as well.