The Google advanced search dialog still shows file types:
But search using the operator filetype: and keywords no longer works. For example, filetype:xlsx attendees returns all sorts of pages.
For now, you can use a workaround: filetype: will still work if your search contains either site: or inurl: operator. We can use them with the minus, essentially excluding nothing, like this:
We all wonder how long Google will support its operators (I will need to update the operator list).
[edited] Danny Sullivan says it is probably a bug.