Classical music recordings upgrade

Abbado with Berlin is always good, Harnoncourt with European Chamber Orchestra is brilliant for modern recordings. Reiner/ Chicago you cannot go wrong with. And IMO, the best is Furtwangler with Vienna(?) live at the Salzburg festival but you'll have to deal with the recording quality.

The London LP box set is fairly common, just make sure you get british pressings. The sound is very good.

For complete sets:

Barenboim, Berlin Staatskapelle on Teldec, the 1963 Karjan cycle on DG, the Bohm cycle on DG, and the Wand set on RCA are my favorites.