I carry the Op/Tech plastic bag-type raincoats. They're cheap and protective, but you can't see through the plastic well at all to see the LCD. Here may be better choices, I've tried and handled all of them.
Canon ERC-E4S This was my favorite. It's made of light waterproof nylon, the lens tube closes with Velcro on an elastic strip. Very snug. There is a clear window in the back, and a fixed sealed eyepiece which fits the 7D and Mark III, and an adapter for other bodies. No possibility of a leak. It's very cool to have something that's made for Canons only. There is a clear window which you can coat with a plastic cleaner or spit or toothpaste or Mr. Clean Magic Eraser to prevent fogging. The best thing is that the material is meant to drape over the camera and head, and extends 6"-12" over the legs. It means you can get both hands under to manipulate the body. That was my biggest complaint with the others, only right-sided dry control. The Canon material is thin enough that you can use this on a 24-105, and a 100-400L, @400mm with no problems at all. It folds to an 8.5 x 3" roll, and comes with a pouch for travel. It's very light, just a few ounces. This one may tear the easiest (hey, that's why God invented Gaffer's tape), but it's the easiest to work under, configure and pack. And it's the color of a white lens. Drawback is that the window shows no detail in the LCD.$89.95
Aquatech Sport Shield F/200 This was my next favorite. Made of slightly thicker nylon than the Canon, it fits tightly around the camera and lens via zippers and an elastic sewn into the fabric near the bayonet mount. It has a clear window in the back, and the a neoprene hole to stretch around the eyepiece. A Thinktank eyepiece will work just as well as the Aquatech. The problem is that it has only a rightsided arm sleeve. If you want to preview an image, you have to press the button through the plastic screen. Very well made, but I didn't like that single arm hole and the inability to control the left side of the body. Again, difficult to make out the LCD through the window.$149.95
ThinkTank Hydrophobia 70-200 This was the most complicated piece of business of the whole bunch. It has a zipper; multiple Velcro tabs; a strap to hold it to the lens from the inside; a strap to hold your camera strap on the inside!!!; a Velcro/Neoprene band around the lens near the hood; very heavy material, the best of the bunch. But though it was fine with the 100-400 (or a 70-200), scrunching up and pushing back the fabric made it really hard to use with a 24-105. The heavy fabric makes it bulky and it takes up twice the room in your suitcase as the Aquatech. It has a Neoprene hole for the eyepiece that you stretch around the eyepiece as with the Aquatech, but it has a plastic flap above the eyepiece to keep it dry when not in use. However, because of the placement of the Neoprene hole and the flap, the plastic window is obscured and I really couldn't make out the details of the back of the camera! It too has only a right arm hole. Plenty of buttons and straps, but what a pain in the a$$ to get on the camera...and then you can't see the back. And the plastic window is as bad as the others. $139.75
LensCoat Rain Coat This is a pretty decent cover. Waterproof material with a right arm hole and the camera back open, that is, no isenglas semi-transparent window. The advantage here is that you can see exactly what you've shot in the LDC or in Live View, as there is nothing between your eye and the camera. Not great in a downpour, but for hand held and tripod shooting, it's otherwise excellent. Very well made, many camo patterns, light, thin, strong material.
After all, I got the Canon for downpours, and the Lenscoat Rain Coat (not the Raincoat Pro) for other rainy shooting. LensCoat makes a product called the Rain Sleeve, which is like the Rain Coat but with a drawstring at the hood rather than the Rain Coat's elastic Velcro band, and no right arm hole. It's cheaper and adequate, but the right arm hole actually makes carrying the camera in the rain easier when handheld, and adjusting the buttons much easier.
