calorie-count.com has a good "recipe analyzer" section.
As far as desserts Passover time. Yeah, it's tough. Actually it's tough other then Passover too.
How about a good old fashioned fruit fruit platter? Fresh sliced pinapple, grapes, mango, strawberries. You can even dip a few of the items in some melted chocolate chips if you like. There's also meringue cookies which are basically egg whites and sugar. Not exactly low cal, but..... There's also sugar free jello. You can serve it with the fruit.