Personally, I think one of the best ways to explore classical music is to just invest in a big, high quality box-set/collection for each composer. It means that you don't have to buy millions of different albums, which avoids duplicating stuff you already have, and in the long run it's much, much better value.

For Chopin, this complete piano edition is extremely good value and has lots of excellent recordings from good pianists.

If you like Chopin, there's a good chance you'll enjoy his even more virtuosic friend and fellow composer Franz Liszt. This collection provides a good overview, although Liszt was extremely prolific so there's always more to explore.

If you like both of those piano specialists, you might also enjoy Robert Schumann, who was from roughly the same generation. This collection is excellent but Schumann can be a bit of an acquired taste, so if you just want a sample, I'd recommend this album as a good starting point.

For Debussy I'd recommend this collection. If you want to explore his orchestral and chamber music as well as his piano work, this complete edition might be the way to go.

For Beethoven, I'd recommend getting the complete piano sonatas. There are quite a few complete sets - personally I'd recommend Brendel and Arrau. My favourite complete set is by Paul Lewis, but unfortunately it doesn't seem to be possible to download the complete set in one go - you either have to get the different volumes separately or get the complete set on CD.

If you want to move out from there to other piano composers, then Brahms, Rachmaninoff, Schubert, Mozart, Ravel, Satie and Fauré are all great. I could make some more recommendations for them but I think I've probably already given you more than enough!