Gede: I recall F15 Strike Eagle 2 and LHX.
Gods, from the Bitmap Brothers also had excellent sound on PC Speaker.
I don't recall playing Wolfenstein 3D with the sound card.
SirPrimalform: Monkey Island 2's internal speaker intro music is surprisingly good.
To me, using a sound card to produce music was just like producing regular music. You had an orchestra and you were a regular composer / maestro.
But creating music for that little limited piece of hardware that was meant to just do "beep", was as if you were mastering some mysterious art. The gurus could take this known quantity and make wonders with it. An electric tune, a full score with what seemed multiple instruments, lasers firing, people screaming, glass shattering, even some recognizable speech (where is the awe when you hear recognizable speech when using a sound card?).
I think it was about exceeding harsh limits. Like the Assembly Demo Scene. 4K?
This is crazy! Of course, now they allow 3D cards, so we get more amazing stuff. But the old CPU-only DOS intros are my favourites.