Ok, so the sad commentary thread inspired me to want to learn more about classical music. .................
This is really a tall order, Josh. So this list will go on for a loooong while perhaps when all the people reading the thread kick in their 2 cents. Lone Wolf gave a big list in the other column I think. May be let's go one thing at a time. I'll start with Guitar Concertos. You gotta pick up John Williams's set. The supreme master of the guitar of course is Segovia. But, his recordings are not quite audiophile. John Williams Segovia calls the prince of the guitar, so you can figure out. Columbia even issued one in SACD, tho I think the SACD is not as good as the redbook version. Rodrigo's Aranjuez concerto (with the Philadelphia Orch., Eugene Ormandy) you probably know. Fantasia para un gentilhombre you'll love also. Another American, Christopher Parkening, is also a great guitarist.
You said your wife likes Beethoven's 5th piano concerto. Who wouldn't with the emperor of piano concertos. If you desire the whole set, probably Leon Fleisher's set is excellent. He's been out a few years with hand problems. But, somehow miracles happened, and he has resumed his career, tho probably too late. He's from the Beethoven/Carl Czerny lineage. Can't go wrong. I think I had posted in the other column, Beethoven's 4th is just as swell.
I'm sleepy-eyed, but another thought. Violin concertos. Pick up any Arthur Grumiaux recording you can't go wrong. His Beethoven violin concerto is the best in my book. His violin sound first of all is gorgeous (of course credit partially should go to his instrument, one of the better Strads I think). The one particular one I have in mind is probably hard to find. It's not the verison with Sir Colin Davis (that's a Penguin must-have recommendation), but with another conductor (both on Phillips though). The sonics on that particular one I haven't heard better, tho it's an old recording. His violin has that vibrancy I can't find in any other recording, tho the others may be more modern in recording technology, etc. Say Joshua Bell is a current American favorite violinist, but his violin sound is thin, much thinner, compared to Grumiaux's. I have in my collection at least 5-6 recordings, Arthur Grumiaux's earlier one is still tops. Such others as Yehudi Menuhin, Heifetz, etc. may be technically fantastic, but sonically they're short, IMO.
Until next time, happpy hunting. Classical music is a deep treasure chest. You will never exhaust finding gems therein.