For weddings, a 5D MK II might be a good choice. Often, you can't use a flash, and you need not only low light capabilities found in full frasme bodies, but the 5D MK II's ability to focus in low light. I'd only use the center point with this camera, but the center point is very good.
You can often find a good used one at the Canon site. They do run out quicklly, so keep an eye on it. If you can find a old Canon film slr or broken posershot, its good for about 20% off a refurb thru the Canon Loyalty program, which drops the price with tax and shipping to about $1500. I have my old camera here and am waiting
As for lens, a 35mm L and a 85mm f/1.8 will supplement your 50mm nicely. I do not recommend anything slower than f/2.8, and without flash, thats marginal. Your 18-135 is a outdoor lens, keep it at f/8 and it will do reasonably well.