This homemade rain jacket was made in 2005 and did not weigh more than 250 grams, pretty light at the time.
Haglöfs Oz was one of the world's lightest rain jackets, especially since it was made from Goretex Paclite, in 2007. 196 grams for a size XL. Best rain jacket I have ever had. Expensive.
My current rain jacket, Marmot Essence 2010, weighing 210 grams or almost the same as the Oz. Not very expensive. I have a matching pair of rain pants from Marmot as well.
An excellent jacket that is reasonably light and does not cost much, Packaway from the Swedish mailorder company ITAB. It might be found in other countries and under other names as well, I do not know. Weight 270 grams in size M and the price 398 SEK (Swedish crowns).
Even lighter and even cheaper. DriDucks costs about US $20 and weighs only 170 grams. Not durable, though.
Comments and current insights: If you live and hike a lot in a cool and rainy part of the world, like I do, the rain jacket is important for comfort and safety. But if you focus on it being RAIN jacket that you use as little as possible it need not be heavy or sturdy. Or hip. That way you can save a lot of weight and money. Combined with a windshirt for wind protection the examples above still weigh less than most shell jackets, be they 'soft' or 'hard'.
The homemade jacket above served me well for several years. It was made from three different fabrics. The shoulders, where the rain falls hardest and the shoulder straps rubs it in, where made from Goretex Paclite. Arms and lower chest was made from a lighter waterproof/breathable than Paclite. For the hood, back and from the waist down I used non-breathable but very light silnylon. The back area is mostly covered with a pack and will not 'breathe' much through that. The jacket worked very well and won me many friends because it was so outstandingly ugly. One arm started leaking on a wet trip around Glacier Peak in Washington, USA and was retired.
The Haglöfs Oz has seen a lot of use, both on the trail, in the brush and on the street. It has never leaked and is still working very well. I know of other people who are less satisfied with the Oz. Perhaps another year or another batch from the manufacturer.
Marmot Essence has so far withstood one rain storm and quite a bit of regular rain without leaking. I also wore it, contrary to my general principles, for several days when it was not raining, but very chilly. More on that hike here. It seems to breathe very well and showed no condensation on the inside. Mind you, I was not sweating much...
About the cheaper rain gear I can recommend Packaway for any kind of hiking. Driducks break very easily; I would not use it for hikes off trail but I imagine that they could be patched with duct tape and so function without ruining a hike or land you in danger of exposure. There are other light and cheap rainsuits; I do not plan to be exhaustive but only to cover gear I have used myself. And always test rain gear in the shower when you have bought them. Something sold as a rain jacket that leaks is by definition not a rain jacket and should be returned. No matter how light or how heavy.