I have made a lot of dioramas in the past using these products at one point or another :)
The vinyl tiles from Home Depot or Lowes. They come 12x12 inches, different styles and they're fairly cheap. It's my top favorite. The carpet is another good one. You have color variety and you can get small cuts, also from the hardware stores.
The fabric is a new technique for me. I applied it to a diorama I'm working on and I'm really liking the outcome. So, I thought it was worth a mention.
The shelf/drawer liners are a great floor option. Love the thinness and how easy they are to apply.
Scrapbook paper is perfect because it's limitless. There are so many options and they're great for walls too!