I tend to find that the denim on both top and bottom works best for people in occupations that demand it (e.g. railroad worker, rancher, etc.). For casual dress, I prefer denim on either top or bottom but not both at the same time.
I wear denim jackets when I'm wearing casual trousers, twills, etc. on my legs. I recently acquired a slim fitted, rigid indigo trucker jacket from Levi's that goes with pretty much anything. Deep indigo is the perfect compliment to earth toned trousers. I haven't washed the jacket yet, as I'm hoping to have a similar fading effect that I also go for with jeans; I plan on waiting as long as possible before that initial wash.
I also have a suede jacket of unknown brand (got it off eBay and there were no tags - could be a one off from a skilled worker) that is an exact replica of the slim fitted Levi's trucker jackets. It has all the style of the denim trucker jacket, but the material being a tan suede allows me to wear it with jeans without going off into what I've heard others call the "Texas Tuxedo" look. It's perfect for casual wear and dressy enough to wear on a date (the suede gets compliments all the time). The suede gives it that elegant appeal and the style (slim trucker) is a familiar classic cut that is instantly recognizable without being cliche. I love it so much I feel guilty that the denim jacket isn't getting as much wear as it deserves.