I'm often asked what equipment I use - both by other photographers and wedding guests. I'm always happy to talk "gear" with people, but it needs to be stressed that owning the best equipment does not make you a good photographer. My advice to people is always to only buy new kit if you find yourself being limited by your current kit. Use what you have first, then once you know exactly what else you need, buy that.
For most people, the first and best thing to spend money on is high quality lenses. It doesn't matter how many megapixels your camera has if you put a cheap lens on it, the quality of your pictures will suffer.
As a wedding photographer who shoots almost entirely using available light, I need lenses that can shoot high quality pictures in very low light - so I mostly use fast aperture prime lenses.
From left to right they are the 24mm f1.4, 35mm f1.4, 85mm f1.2 and 135mm f2. These are the best lenses Canon make and allow me to shoot sharp, high quality images in very low light.
I also have three zooms.
From left to right, the 17-40mm f4, 24-105mm f4 and 70-200mm f2.8. Again, these are all top quality Canon lenses. They're sharp and fast but, with smaller maximum apertures, they're not as useful in very low light, so they're mostly used as backups to the prime lenses.
I've purchased these lenses using the advice laid out above. I started off as a newspaper photographer using mostly zooms, but as I moved more into shooting available light wedding photojournalism, I figured out what equipment I needed to allow me to shoot the pictures I wanted, and bought that.
Its easy to get sucked in to buying lots of cool stuff you don't really need. There's always a new camera/lens/flash/gadget being introduced that promises to be better than what you have. But if its not going help you to take the pictures you want then its better to save your money for something that will.