Flimbo's Quest - Reyn Ouwehand
The melody and instrumentation may be saccharine, but Flimbo's Quest also shows off just how well the SID could thump its bass. The structure isn't amazing or anything, but there is a bit of theme variation to keep an ear out for. Most of the joy here is in how full the SID sounds compared to other competitors such as the NES' 2A03 or the Atari 800's POKEY.
Cybernoid - Jeroen Tel
This is one of the few Commodore 64 games available on Wii's Virtual Console, and it's not a bad idea for a game, but the end product is too frustrating to take seriously. Anyway, Mr. Tel here does a good job of demonstrating how well SIDs handle the crossroads of moody and dancey. The drums here will keep you going while lingering tremolo notes ponder high school-quality philosophy. Stick around until 4:51 for a melodic treat.
Monty on the Run - Rob Hubbard
At 0:33, a methodical, foreboding intro finally creeps its way over the ledge of a cliff. Its fall is broken at 0:37 by classy SID drums, and the whole song is set in motion. From here, the melody is more or less strapped to the back of frantically--though regularly--paced drums. Notes vary a little in length, but notes that stray too far from the normal length are only used to punctuate phrases. By 1:45, we've had enough, and the tune lets up with gradually longer notes and a lower pitch (compare it to 0:39). Finally, we're let off the ride at 2:06, ready for another go 'round. The tune seems to be going normally until it runs off the tracks at 2:40, resulting in a guitar solo at 2:49. Monty on the Run already has a good melody, and this solo is okay, but its placement and production put it over the top. It's hardly out of place, but it is a surprise, and it strikes a strong contrast to the tightly-structured first half of the song, which felt married to the rhythm. There's also new liveliness in its production, since it shows off long, winding pitch bends unheard elsewhere in the song. (And if that wasn't enough to top things off, try the violin solo at 4:51.) Chiptune instruments commonly take after real world instruments, but rarely are their identities conveyed as strongly as the ones here. Between that and the diverse structure, this is Rob Hubbard's most impressive SID; it may not be his best, but it scratches the most itches.
I regret not knowing enough about these guys to comment on their general style, but this should at least give you an idea regarding whether or not you're interested in SID.