Here's my take on this, as well as the so called people who think that diet along provides it all.
First, multivitamins are certainly better than no vitamins at all, but just like anything else, I prefer packs that provide you with the vitamin as individual as possible. I don't think I have to quote a scientific study to reasonably believe a Vitamin E pill will give me a better form of the vitamin than some magic pill with 80+ vitamins all at perfect levels. In fact the multivitamin is too small in most cases to provide the volume of nutrients that I think is missing from the average american diet.
I'm a big fan of convenience, so I use some from healthy n fit that has like 12 vitamins in a pack. Each vitamin serves a specific purpose in the pack, not 12 multi's. There are many other multi-packs that are great as well. Now your body can't possibly absorb that many at one time, so I take half in the morning (with food) and the other half at night (with food). I would encourage you to go this route.
I have run into a lot of people who claim you get it all through your diet, but who are they kidding. You're diet would have to extremely specialized to get the proper balance of everything every day. I don't care if I piss out 95% of my vitamins on a day when my diet provided me with what I needed, but I DO care if I don't have enough of what I need on those days the diet doesn't get it done.
One thing I can tell you as well is that I feel better when I take them from when I don't. I also seem to recover a little faster as well.
For my Omega 3, which you don't tend to find in multi's or multipacks, is through eggs. You can buy eggs from Kroger with 660mg of Omega 3 fatty acids in them. I boil those bad boys and eat them. Eat them however you want, but that's my preference. You also get the GOOD cholesterol from eggs as well as a generous 6g of protein on average from each egg. That's a lot from something you can eat in one bite. I eat them as a late night snack food while I'm gaming or watching tv.
I also bought a little package of flax seeds. I throw them on random meals to get those in. I'm not overly worried about getting the perfect amount of these, but I use generous helpings when I do use it.
If you want a link to the vitamin packs I use, pm me and I'll send you the link, been real happy with them. Available at most gyms and stores too.