I made my first batch as a brown ale with pumpkin spice. Brewed it Labor Day weekend last year and it was ready the week before Halloween. It was pretty tasty.
After that, I brewed an attempted clone (it turned out well, but definitely not a clone) of Sam Adam's White Christmas which is a Belgian wit with holiday spices (cinnamon, nutmeg, and ginger). Then I brewed a Belgian Trippel with orange blossom honey and orange peel. My last batch was a snowshoe Porter with vanilla beans added in secondary.
So yes, you can add pretty much anything that's edible. It's up to personal preference and taste. One word of caution, go easy on the spices at first. A teaspoon of spice goes a long ways. One or two teaspoons is usually all that's needed for a 5 gallon batch. And for fruits and spices like vanilla beans that need to soak, start them out for about 5 days, and then sample it daily until you hit your desired taste. Before you add that stuff, make sure you'll have time in the next week or so to bottle or keg. Once you hit your taste, it needs to be racked off the flavor item.