Look for the USP label!
The best way to get all the minerals and vitamins you need is through your diet because supplements don't have all of the good phytochemicals and antioxidants and fiber and stuff that you get from eating real food. That said I take multivitamins during cycling season because I'm really pushing myself physically during this time and am not sure I can eat enough to give myself all of the nutrition that is optimal for performance and recovery.
I think it is best to avoid "specialty" multivitamins....like the ones for women or folks over 50, etc. In my opinion those products are a marketing ploy to charge you more. My doc tells me to avoid multivitamins that contain more than 100% of the daily recommended value for a particular mineral or vitamin and to use brands that have the United States Pharmacopeia (USP) symbol on the bottle. If the brand has been USP verified then you know it is what it says it is and that it will dissolve appropriately when you ingest it.
-traveller
"It never gets easier, you just go faster." -- Greg LeMond