Off top of my head, Holland is probably next fav followed by Endless Summer. However, after reading about your goals in adding to your collection you may want to keep your expectations at less-than-stratospheric... For quite a while the primary sound/recording target for Beach Boy stuff was pretty much the car radio - and that was back when there was a single radio speaker in a car. That's some of why so many of their albums were mono and why re-engineering/re-mastering those releases are a real challenge. You probably need to keep your expectations somewhat modest if you're hoping for stellar sonics - the songs can be quite good but there's just so much available in the source media.
