How to make Spotlight ONLY index certain file types? I use my mac for development, and create/delete so many (big) files that I ended up turning Spotlight off, since it was taking so much time indexing these files.

I think it would be fine if I would only allow Spotlight to index pdf and doc documents, is this possible?
As there is no easy way (no GUI certainly) to exclude file types, your best bet might be to exclude specific directories from being indexed. Create/delete Your big files inside one directory (including subdirs) and go to Preferences -> Spotlight -> Privacy and choose Your excluded directory (You can also drag and drop it).