I guess it's no surprise that I have too much to say on this one

That's a great point, BSQ, about the % of RDA and the number of calories. I'm so glad you mentioned that. DietPower is letting me have 2000 calories now because I'm so large.
About vitamin C--like calcium, you can't absorb more than 500 mg at a time apparently. Even the Linus Pauling Institute (the guys who came up with the idea of taking a lot of C) are now recommending no more than 500 mg at a time). So you might have better results from splitting your dose up (if you aren't already).
What follows is what I mean to take and what my thinking is. These are not recommendations for anyone else (except the multi). My doctors know I take them, but I did the research on my own. And I guess I have a cast iron stomach because I don't seem to have many problems.
1. Multivitamin
For several reasons. One is because I'm not in control. Another, and the most convincing, is that, though they thought that a multi wouldn't help people with basically balanced diets, in fact, the massive longitudinal nurses' study is finding that taking a multivitamin, any multivitamin, increases your life and the quality of life. Especially as we get older (but also with the digestive changes of menopause, I suspect), we absorb less and less well, so the insurance of a multi apparently is worth it. I take one that offers 100% of the RDA of lots of vitamins and minerals. DietPower has shown me that even basically balanced eating doesn't balance nutrients that well. And 100% of nutrients plus diet isn't going to be too much because RDA is fairly low.
Like BSQ says the real concern seems to be vitamin A and iron in multis. It's better if most of the vitamin A is coming from carotenes (mixed or beta) and if the iron is low (it's an oxidant so more is not better--though obviously you need enough).
2. Selenium
Though in this case, I only take extra selenium if I don't have any Brazil nuts on hand. Selenium is a powerful antioxidant--so it protects against heart/artery disease and cancer. More important to me is that it's necessary for thyroid balance. It's essential for the conversion of T4 to T3 (synthroid to the effective form, in other words), and I really do think it makes me feel better. Because I have hypothyroid, I figure the RDA is too far below the recommendation of 200 mcg. And it's hard to get from diet unless you live where the soil is rich in selenium and you grow your own veggies (or eat two Brazil nuts a day).
3. Calcium Citrate
I actually don't take that much calcium. DietPower has shown me that I get a lot from my diet and you can get too much. So, I take a pill with 500 mg a day and check with DietPower at the end of the day to see how I've done. Calcium is now added to lots of foods, so Prevention etc. are warning about tracking the amount. Since this is for insurance, I do take citrate, which is absorbed better.
4. Magnesium
I try to take 600 mg of magnesium in addition to the multi. A guideline is that it should be half the level of calcium for calcium to work well. I take it because of what I've read about bone health. But even more, I clearly have deficiency symptoms, and estrogen creates deficiencies because the liver uses magnesium to process the estrogen. It's hard to get enough from an American diet--it's mostly in beans. This is a case where I clearly feel a difference. I start to get aches and pains without it. It clearly improves my mood (I suffer from severe clinical depression). Having gone on and off and on using it, I know it makes a difference.
5. An extra B complex
I take one where all the B's are 100% of RDA, so that each has the proper balance in relation to the others. And I take more than my multi again because estrogen creates deficiencies in folic acid and B6--and again I have so many symptoms of problems with these. Also, the puzzle over taking estrogen and whether it helps heart health involves homocysteine levels. And they lower homocysteine levels. So my personal theory is that the problem with HRT and heart health rests in part with the deficiency. Since heart problems are the health issue in my family, I take extra B's at night (multi in the morning). Also, they improve depression. And they are toxic only at extremely high levels or when out of balance for extended periods of time.
6. Evening primrose oil
If you're missing a particular enzyme, there's no real other way around it except EPO. And I'm clearly missing it. When I don't take EPO, I lose hair and I get excema. If I take EPO, I don't. It's also good for a lot of other things--like aches and pains and mood.
7. Natural vitamin E
400 IU is recommended. It's needed to make the EPO work well, but it also affects a lot of other things that ail me and is a powerful antioxidant.
8. Fish oil
If I haven't had salmon or tuna that day. Again, I started because it makes the EPO work well, but it's good for depression and hearts etc. Flax seed is no good because it also requires that missing enzyme, so, since I know the EPO works for me, I know that flax seed won't help me (besides it's way too laxative for me

)
9. Milk thistle
Between being obese and taking oral estrogen, I have fatty liver intrusions. I read in the medical journals themselves what could be done to prevent liver function damage and even losing weight might not help. And in fact rapid weight loss makes it worse. There's actually been quite a few small studies on the active ingredient in milk thistle and the liver and that it prevents further damage.
What I don't take extra of--
Well lots, honest
But I don't take extra Vitamin D--it's in my multi, it's added to foods, and a small amount is in my calcium citrate. You can get way too much of vitamin D, which is a bad thing. AND vitamin D is actually a hormone and interferes with hormonal balance.
And I don't take extra zinc. It's another thing that estrogen creates deficiencies in, but it's easy to get too much and I have some in my multi. Now that I have DietPower, I track the zinc, and pop a small amount if it shows that I didn't eat enough to be over the RDA.
It seems like a lot, which is why I stop taking it now and then, but each piece fits a very particular health issue that I have. If I didn't have particular health issues, I'd probably only take the multi and calcium/mag.