We are also doing a 3 tiered anniversary cake this weekend ... for my parent's 35th. The bottom 14" layer will be Pilsbury HInes Devil's Food mix w/the Durable Cake recipe (Jello Chocolate Fudge pudding) .... filled w/chocolate buttercream.
The middle 10" layer will be white chocolate w/raspberry creme filling (Smucker's jam mixed with buttercream). Using Pilsbury white cake mix with a box of Jello white chocolate pudding.
The top 8" layer will be lemon with strawberry filling (CK pastry filling from sugarcraft.com). Was going to do Bavarian creme, but I think we will just stick with lemon/strawberry - seems to be a popular combo.
Making a 3d cake "on the side" for my Dad, who is a classic car collector ... bought that Wilton 3d car pan and am trying to figure out the best way to decorate it. May just glaze it w/melted white fondant instead of doing the buttercream "stars" all over it. Can use piping gel for the winshield & windows I think. Anywhoo, this cake will be pistachio w/no filling
If you don't want to bake three separate flavors, you could always do all three layers as white cake with a strawberry layer, a lemon layer and a chocolate/almond layer.