We listen to oldies and Motown a lot while riding.
We have a biker hangout near us, Defiance MO, and sometimes while riding through we'll be listening to Disco and crank it up so all can hear. I can only imagine what some of them think.
I have over 148k songs in my iTunes. Some are duplicates because of greatest hits and special releases etc of the same group, but I've never deleted them.
I have from classical, rock, some hard rock (but not heavy metal), tons of blues (new and old style), Motown, instrumentals, all of the Ventures albums to pop. I have a lot of Sinatra, Louis Armstrong, Dean Martin etc. Some country, but no Rap. I'm not a traditional country guy but like Alabama, Restless Heart, Exile (even when they were pop) Judds, etc.
I ride with a 16g iPod and most of it is oldies by years. I still find it easier to use the iPod than stream with my XM as I have control over my song choices with the iPod.
I have the stock head unit in my '09 SERG and have upgraded the speakers to the J&M 7.25". I'm sure that I could get more sound, but with just the speaker upgrade we can hear the tunes just fine.