Fruit bowl. Buy your favorite in-season fruit. Cut up and put in a pretty glass bowl so that you can see the fruit through it.
If you have time, you can take a watermelon, and instead of cutting it in half, cut like a basket/bowl, e.g.:



If you have time, use a melon baller and scoop the insides out into balls. You can also do this for other melons, e.g. the third photo
I think that berries make a fruit bowl look fancier, especially the big berries that you can often get around now. Also, I find that mandarin oranges make it look fancier, too. And mixing colors also makes it look fancier.
Sometimes when I do the glass bowl, I'll take slices of pretty fruit (like kiwi, strawberries and bananas) and stick them to the inside of the bowl before I put the fruit salad in to decorate the bowl.
Time consuming, but does not need a lot of skill and definitely looks fancy.