There are several 2WD-friendly trails in Anza Borrego that you can do. Look back through the Pictures section here or check my gallery website if you want to see what they look like (or, better yet, get a guidebook).
Mine Wash - off of Hwy 78. Very scenic, with some nice camping spots along the way.
Blair Valley - except maybe for the little dead-end spur at the far northwest corner. I've seen BMW sedans parked at the Pictorgraph hike parking area, and the rest of it is pretty hard packed. Very scenic.
Clark Dry Lake - off of S-22 at the north end of the Park. You can go about 10 miles up this road. You'll know when it's time to turn around. Don't drive on the actual lake bed, other than the clearly marked trail across the top edge of it.
Outside of Anza Borrego, another nice drive is Palomar Divide Truck Trail, off of Hwy 79 near Warner Springs (not too far from the Pie Company in Santa Ysabel).
These are all the sort of places you don't need to wait for an Xcursion, just go out and do it. Or, post up here and see if anyone else wants to join. The nice thing about these is that they are all very scenic, and it doesn't usually matter if you're 2wd or 4wd, as long as you exercise common sense.
