All One brand makes a good powdered vitamin, different variations. If you email them, or even call, they will send out a free sample packet (or at least they did for me a couple of years ago). In the US, the Vitamin Shoppe carries their products.
However, I got tired of the mixing, and am unable to drink much at once, so I switched to a liquid vitamin supplement. Nature's Way brand: Alive. This one is available as tablet too, but not powdered. I purchase at Whole Foods Markets, but it is available online and perhaps other local outlets.
Besides this, I take COQ 10, E, resveratrol, and a fish oil. Personally, this is all I'm really committed to taking each day, although there are many people who take additional. I'm at my limit because of difficulty in swallowing them. Also, although not a supplement, I add a half dose of generic miralax to my coffee each morning.