Here's the first road that boothguy mentioned. The destination is Mt. Palomar. Coming from I-15 South take the SR76 exist and then go southeast on SR76, from the upper left of the map, then take either the first road (Nate Harrison Road) or the second road (Mt. Palomar Rd/South Grade) off SR 76 to get up to Mt. Palomar. You can then come down either road, or take State Park Road and East Grade Road southeast all the way down to Lake Henshaw, then return west on SR76.Also: since I'm thinking of taking my new 328i out on some drives around here in Southern CA, where is this road in San Diego County that's good? Heck, what ARE some good drives around here?
Here's the second road that I mentioned. From Julian, take it down to Banner and then back up again. This one is short, but intense, and possibly less traffic.
If you've got all day, you can combine them. The roads between Mt. Palomar and Julian are all pretty enjoyable! A good return home would be to take SR79 from south of Lake Henshaw up through Warner springs back to I-15 North back to Orange County.
These are both AWESOME roads and I've done them both many times in my S2000. Mt. Palomar is particularly attractive to motorcyclists and you'll see a lot. Traffic can sometimes be bad and extremely frustrating when you're stuck behind someone out for a Sunday drive and going 30 MPH all the way up without pulling over. I've convinced that some people, possibly local residents, do this on purpose to combat speeders.
I'm looking forward to doing them in the 335is when it arrives home!