Yeah, I like a mix of anchos and guajillos, at the least, for my chili. Anchos give a nice deep, earthy flavor, without being too spicy. Guajillos add another type of fruitiness to it with a bit more of a kick. (I think of anchos as being a bit pruny-raisin-y, and guajillos a bit more berry-like, but with some tannic astringency, too, if that makes any sense.) On top of that, if I want some more kick, arbols, piquins or cayennes for that sharp spice kick, and perhaps chipotle or morita for smokiness. Also, I like just plain ol’ Hungarian paprika in the base, as well, to add flavor, color, and red pepper sweetness to it without heat. Beyond that, cumin and oregano are essential, as well. I go back and forth between regular oregano and Mexican oregano (which is a different plant than Mediterranean oregano and has a different, more citrus-like flavor.) Then garlic and onions.
Or, if I’m lazy, just straight-up Gebhardt’s chili powder + cumin.
My preferences and approaches change a lot, but these days, I actually just like the approach of all dried chiles, no fresh chiles, to give it a deep, earthy taste. But feel free to use fresh chiles and fry them up with your onions or whatnot. I like to bloom my chili powder in the oil for about half a minute to a minute for the flavors to marry with the oil. I add this usually after frying up my onions & meat before adding tomatoes (if using) or beans (once again, if using.) I think it makes a good bit of difference to bloom the spices.
But chili is a wide open canvas to modify to your heart’s content. If you want ideas for “secret ingredients,” chocolate, cloves, coffee, cinnamon, are all fairly well-known not-so-secret ingredients. Or using a lager or stout (something not hoppy) as a liquid base–that’s pretty standard. You can use masa for thickening and adding a corn flavor, as well, or some people even add crushed tortilla chips or even Fritos. Just have fun with it. I also like to do mine all-beef, but with a combination of ground chuck and hand-cut boneless short ribs or chuck that’s been cubed into about 1/2-1 inch dice for textural variation. If using beans, I actually prefer navy beans, pinto beans, or something of that nature vs. kidney beans.