I keep my processed film in archival storage pages in 3-ring binders, and I do the same with my processed slides. My slides are all numbered (AA00-99, AB-00-99, AC00-99, ..., ZZ00-99, AAA00-99, etc.) so if I create a slideshow, I simply document the slide numbers and can recreate it from the pages. (I don't store slides in trays unless I plan to redo the show soon.)
I use PrintFile pages because they are easy for me to get and reasonably priced. They seem to be made in Orlando, Florida.