To get you started, I have included some of my favourite SID tunes in the
subdirectory Example_Sidtunes
of the KSidplayer distribution:
PSID.Dance_At_Night
PSID.Final_Synth_Sample
PSID.Shades
PSID.Synth_Music_Gen_85
PSID.Some_Pleasure
PSID.Guy_Shavitt-2
PSID.Guy_Shavitt-4
PSID.Weekend
Trifle
Taboo-1
For a large collection of SID files, check out for example the High Voltage SID Collection (HVSC) at http://www.dhp.com/~shark/c64music/.
The next section High Voltage SID Collection FAQ contains the Frequently Asked Questions on the High Voltage SID Collection.