I'm not working right now so I'm going to haul a buddy of mine out to CO for a quick road trip in the next few weeks. The thing is I want to drive my BMW Z4. Outside of Guanella Pass or Loveland are there any other trailheads in the front range that would work for my car? He has no experience so Guanella or Loveland would be a perfect but I've been all over those options so something new would be nice.

Longs TH is paved, as is most everything else in RMNP (except Fall River Rd, but it's easily passable in a passenger car).

Pikes Peak (Barr trail) TH is paved.

Looking for a 14er, specifically?

The Avalanche Gulch TH for Mt Yale is paved, Summit Lake or Echo Lake for Mt Evans, Maroon Lake, and as Chris said, Longs and much of RMNP. For non 14ers there are some in IPW that are paved, most of the Gore THs in Vail, Ptarmigan Lake (west of Yale on the way to Cottonwood Pass), Ditch Trail in Snowmass Village, and in general the paved mountain passes have parking areas at their summits.

There are several paved roads, but then the parking is not paved - i.e. LaPlata, where the road is paved but you park off of the pavement in the dirt. Several others are well graded gravel very close to pavement. Not sure about the Z4 on those though, they tend to have a little lip right at the pavement/dirt transition that you might scratch a bumper on with a sports car.

edit- the South Elbert TH is paved too, but you then have to walk up a 4x4 road for 2 miles, I have used the paved TH in winter when the road isn't plowed and it makes it a longer mileage day, but the road hikes fast.

I've seen Corvettes in the Herman Lake TH and 911s in the lot at the top of Berthoud Pass, even though they aren't "paved"...