As mentioned above the West Highland Line and Far North line still have loads, as does the Dingwall to Kyle line. Although like elsewhere it is slowly being replaced.
West Highland line isn't so fast but the beat of the joints is still quite pleasurable, from memory the FNL does get quite fast but not been up there in ages - Kyle line is similar if not slower than the West Highland Line. Parts of the Kyle and Mallaig lines both have the short rails in sections as well.
I always felt it sounded better on the cl 156 than it does on the 158 though.
Speaking of which, someone took this video of the *full* journey from Queen Street to Mallaig - a good example of what were talking about is on the section from Glen Douglas to Arrochar & Tarbet - there will be others.
From memory, Girvan to Stranraer also had loads of jointed track, and the section just out of Stranraer itself sounded pretty fast on a 156. Not been there in ages though.
There's some sections on the Cathcart Circle lines as well, although far less then previously. Line speeds are only upto 40mph. Sometimes gets used for main line diverts though.