Apiinvert - glucose-fructose syrup for feeding bees. Best results in early spring, for stimulation. The bees will consume it very quickly in winter, is not so consistent like honey! So be careful and check the hives if you feed them in fall with apiinvert. Price: about 1 euro/kg.
Apifonda - solid food, is ok to feed the bees in winter, but I prefer to feed them with powder sugar and honey (sugar patties), is more natural. Price: about 1,50-2 euro/kg.
Nektapol - German pollen patties made with pollen substitute. 4,45€/kg.
Neopol - German pollen patties made with natural pollen from Germany. 4-5€/kg.
These are good for stimulation in early spring, after the bees makes at least 1 cleaning flight.
Of course there are other products you can try feeding/stimulating bees, anyway a good nectar flow or a good natural pollen picking is the best "engine" for the bee family to grow.