Mustard - sharp sweetened tang taste
Vinegar - sours up the sauce nicely
Apple Cider/Juice - strong tart flavor, good for actual bbq'd meat, not my fav if you're just slowcooking something, but works awesome in sauce if you're smoking.
Sugar - glue to the sauce, you should always flour/dust the meat with some spices dry first.
Brown sugar - has a stronger / stickier taste to it of sweetness, can replace normal sugar if you want a stronger sauce.
Maple Syrup - stickiness and sweetness, you don't need to add a lot of sugar or brown sugar if you use this, it makes up for it pretty well.
Cayenne/Chilli Powder - Think this is obvious, add what you want for the heat for your sauce, save the bulk of this for the rub but a palm full is fine.
Cinnamon - go light on this but powdered cinnamon sugar is actually really kick ass in barbeque(and spaghetti) sauces.
Onions/Green Onions - Green Onion is a lot sweeter then regular onion, if you're boiling/stirring your sauce before you add it to the meat though, regular onion is fine.
Worchestershire - saltiness/darkens up the sauce a little bit, works well with the ketchup and the meat, you should probably always add this, at least I do.
Salt - you can choose to add this to the sauce, but it's probably best in the rub for cooking the meat, since you want the moisture pulled while you're actually cooking it.
Cola/Soft Drinks/Soda/Pop - can reduce this/boil it alone before you add in any water and turn it into a syrup then mix in the rest of the sauce and water to get a stickier sauce, works good if you're just using regular sugar mostly, can do stuff like Dr.Pepper or Sprite for pork, but Coke/Pepsi is probably the only shit you should ever use for beef, anything else is liable to be nasty.
Lemon/Lime - meh, I don't like this, but they add their own respective tastes to the sauces, if you want take your pick.
Oranges/Orange Juice - this is actually really good mixed in with the average sweet & sour sauce, put the skin into the sauce and all but strain it out after, or just stick a huge peel in so that you don't have to pick out tiny bits + the actual oranges. It'll make it stickier/sharper as it reduces into the mix.
Pineapple - grill this as well if you want, it isn't really my thing so I have no advise.
Rubs - Best to get it at the bulk or dollar stores for cheap cause when you make a bbq rub you tend to waste a lot of the powder. Can do this like shake 'n bake if you're lazy then dump it on a tray and hand knead it into the meat, slap it around, make it your bitch to get it in there. Salt, Pepper, Paprika, should be in every rub, shit like Mustard Powders, Garlic Powder, etc. are other things you can add, this is really upto you to learn what the fuck dif spices taste like, prob. more important then learning how to Sautier.
Paprika: is typically heavy in this for color and smoked taste, smoked red is the best type.
So if you want a sweet & sour bbq sauce, mix up ketchup, vinegar, mustard powder or whatever mustard, worchestershire, brown sugar, paprika.