I make, I think, five frostings: buttercream, whipped cream, cream cheese, and chocolate. The thing about buttercream is that it's just sort of heavy. I really only use it to frost wedding cakes, where a perfectly smooth finish is requisite and fondant isn't on the menu. When making a really simple cake, I often just used lightly sweetened whipped cream, which really is so delightful especially when fresh berries are involved. But it has to be frosted and eaten pretty quickly, as whipped cream is really only glorious when freshly whipped. I've got no complaints about the chocolate frosting or the cream cheese - only they don't go with every cake.
Something that goes with practically every cake is this: mascarpone mousse. It's more dense and fluffy than plain whipped cream and has a longer staying power. It handles added fruit well, but also holds its own. I made a sponge cake for a child's birthday recently and filled and frosted it with this mousse and kids loved it (kids really like simple cakes - and it didn't hurt that I decorated it with chocolate swirls and M&Ms).
I've tinkered with different variations on this filling but have settled on just one that is the easiest to prepare with the best texture and flavor. The cake shown above is a sponge cake, soaked with sweetened espresso (hence the Tiramisu appellation), filled with mascarpone mousse, frosted with whipped cream, dusted with Dutched cocoa and decorated with gently toasted sliced almonds. Here's the mousse recipe. Follow the Tiramisu cake link for that recipe.
Tirmisu Cake recipe
Makes enough to fill one 9-inch, three layer cake
8 ounces mascarpone
1 1/2 cups heavy cream
2-3 T powdered sugar
1 t vanilla extract
2 T dark rum
Measure all the ingredients into a mixing bowl (or bowl of a stand mixer) and whisk with an electric mixer for about 5 minutes, until thick and fluffy. Resist the temptation to consume the mousse wolf mode.
Use it with fresh berries layered between any yellow or chocolate cake. In an pinch, use it to fill those grocery store individual chocolate cookie crusts, and then top with berries.