I have a large collection of CDs and Vinyl. I do not know what is around you, but if you go to your local record store always browse the bargain bin. You would be surprised by what you might find. Keep an open mind and if it looks interesting, listen to it.
If you like progressive, I'd suggest looking into jazz fusion. Return to Forever, Mahavishnu Orchestra, and Weather Report are a few bands that seem like they'd fit in your collection. I trust that you can find out which albums people recommend (I believe all three have self titled albums as their first album, those are as good of a place to start as any.)
Can't go wrong with other prog artists. I used to be a huge Procol Harum fan. I definitely recommend checking out A Salty Dog as it is a nice piece of orchestral rock.
If you like rap I'd say try to pick up a few MF DOOM albums. I have yet to find hip hop than I like better than MF DOOM's early albums.
If you do go bargain bin hunting my advice to you is: if it looks good, buy it! You might find an unexpected new favorite. I once bought Blur's Park Life because I knew about the Gorillaz and the cover interested me. I actually really ended up liking the album.