Plums and nectarine are both fine. The pits shouldn't be given, but the fruit itself is healthy.
Eggplant is on the "not so good" list, it has a lot of tannin in it, which does make birds sick (its the entire reason behind no avocado in case you didn't know). Asparagus can have it too, mostly in the thick stem, so the tips are OK, but the base really shouldn't be fed.
Salt is bad for birds, as is excessive sugar.
Caffeine is bad.
Rhubarb is another of those high tannin things.
Dairy products are not good. Birds are not exactly lactose intolerant, they just don't digest it. Pre-digested lactose isn't bad, like yogurt, but milk is just asking for a tummy upset (and possibly an infection). Cheese is pre digested, but its also very fatty. Harder cheeses have less fat, softer has more.
Meat is OK, fully cooked (well done) and in moderation. Don't let your bird sit down to a steak dinner, but a piece here and there... its protein.
Excessive carbs is the same as excessive sugars (carbs convert to sugar in the body) so they should be fed in moderation.
Green leafy veggies are wonderful, though spinach can bind iron in the body and should be fed in moderation. I think Broccoli does too, but I cant remember for sure off the top of my head.
Also, know that when feeding a pelleted diet that citrus can help bind some vitamins and actually overdose your bird. I try not to give citrus more than once a week due to that, keeping the dose of it small so as to avoid vitamin toxicity.
OK, my lecture on food is over.. sorry. I work really hard to feed these guys the very best diet possible so I learn as much as I can to do that
Athena