Oh gosh - Raspberry is my favorite so I have tried raspberries several ways. I sometimes just add raspberry liqueur, or if I really want the extra raspberry, I will add fresh or frozen raspberry either directly into the ganache after it is smooth or fold in after I whip it. Or I have placed a layer raspberries (or strawberries) in between ganache or used seedless raspberry jam and layered that with ganache. (I really like ganache!)
The picture below (if it shows up) is ganache with strawberries, but it's the same with raspberries.