Here are ones I really like, to give you a variety - although my original statement still stands. I would make the Kleiber recording your first, then branch out from there.
Szell/Cleveland Orchestra - Sony - these albums are actually dirt cheap - you can pick each one up for ~$5 at Barnes & Noble in the discount CD section. Szell's Beethoven symphony cycle is top notch.
Vanska/Minnesota Orchestra - BIS - Great sound, excellent performance. My favorite modern recording.
Gardiner/ORR - Archiv - IMHO, the best HIP Beethoven symphony cycle.
van Immerseel/Anima Eterna - Zig Zag - high speed adrenaline Beethoven, HIP style. I like it, but it is a real outlier, some of the fastest tempos and leanest orchestration you will find for the symphonies.
Jarvi/Deutsche Karmmerphilharmonie Bremen - RCA - another great recent cycle, up there with Vanska, but I prefer Vanska
Klemperer/Philharmonia Orchestra - Angel/EMI - this is Klemperer! Slower, maybe, than some, but not terribly so. The recording is mono, so not as great of sound quality as the others, but with remastering, there isn't a lot to complain about. It was recorded, I believe, in '54, so it was great quality mono.
Those are all the ones I have and would recommend. Each has something different to offer.