So busy focusing on Mountain View that I forgot about Sunnyvale. Hong Kong Saigon Seafood at 1135 Lawrence Expressway is a good Hong Kong style seafood dining hall. Not as good as the original branch in Richmond but still worth mentioning. (Does anybody know whether they got the insurance money to re-open the Richmond location?)
Below is the standard online index for downtown Mountain View restaurants (all within walking distance of each other). That link lists them by type, and shows 12 Chinese currently. I've eaten at all of them, most of them more than 10 times. Of those 12 restaurants, Cafe Yulong (743 W Dana St) and New China Delight (360 Castro St, Shanghai specialties) are widely considered the most elegant among locals who've tried all of them (Yulong for originality -- Shandong province, unusual specialties -- regularly earns "Best Chinese in MV" poll in the Mountain View Voice). Also, Hunan Chili (102 Castro) is known for aromatic hot savory Ma Po tofu and regional "Chinese" Chinese dishes (with "variety meats," etc.) that you don't see on gringo-oriented menus. That restaurant was on a CBS-5 TV special, not long ago, on good-value Bay Area restaurants.
There are not a lot of choices in Sunnyvale. Hunan Gourmet is not bad. Shanghai Flavor Shop is good but only for the fried soup dumplings. Close to this place is Famous Food which I like for fast cheap fresh chinese food.
In Mountain View, if you like Cantonese style cuisine, try Hong Kong or Kirin. I also 2nd the vote for Hunan Chili.
Cafe Yulong in Mountain View. Do not get anything but the ja jiang mien (bean sauce noodles). Really fresh noodles (made in house). Order anything else at your risk. Dumplings are terrible (don't believe the hype)
Old Shanghai Flavor Shop (Sunnyvale) - concentrate on shen jian bao (pan fried doughy version of XLB) and the other small eats/appetizers or noodle dishes. Hole in the wall place/grease joint but very authentic. Hearty (not light) food here, so bring a big appetite and some workout gear afterwards.
Maruichi (ramen) - downtown Mountain View on castro - excellent Japanese ramen noodles and broth. Noodles are made on the premise with flour imported from Japan. Get the pork (tonkotsu) broth or the kuro broth (black sesame oil on top of pork broth). Or if you can take the heat, the spicy miso ramen.
Sushi Tomi - decent nigiri and sushi, probably the best authentic neighborhood sushi bar experience. Good value lunch sets. Very very very very busy weekdays at noon thanks to the techie crowds
Pho Binh (Sunnyvale) - probably the best Pho that's within 5 to 8 mins of MV. Clear but flavorful broth with the right amount of salt, likely no MSG.
Nami Nami (downtown Mountain View) - high end classy Kyoto style dining with relatively cheaper lunch sets that give a glimpse of what dinner has to offer (with dinner easily going $30 or more per person as you try the multitudes of various cooked dishes). Don't bother with anything sushi, tempura, or teriyaki here. Instead concentrate on grilled silvery fish like mackeral or black cod, anything miso marinated, tofu dishes etc.
Shabuway (downtown Mountain View) - Great value for a simple but great shabu shabu meal.
Castro Street in Mountain View is a wonderful place for Chinese food. I'm fond of pretty much everything at Queen's House (which is Taiwanese), but you should also try the northern-style Chinese at Cafe Yulong (e.g. fish jiao zi). The folks at Chef Liu are really friendly. I've also had good meals at Hunan Chili and New China Delight.
Near Castro Street, on El Camino Real, is Shanghai Taste Delight. Absolutely worth checking out, especially if you can read their secret menu.
My favorite Chinese restaurant in Sunnyvale is PF Chang's. Just kidding! Actually, it's Windsor Fish and Chips, on Old San Francisco Road. Good Taiwanese food! Gotta love those pig ears!
I believe the dim sum place in Cupertino mentioned by lj2899 is Pan Tao.
743 W Dana St, Mountain View, CA 94041
273 Castro St, Mountain View, CA 94041
Windsor Fish & Chips
876 Old San Francisco Rd, Sunnyvale, CA 94086
Also, there is a mom and pop Shanghai-style restaurant on the corner of Rengsdorf and Central that is really good. It is behind the Shell Gas Station. I don't know the name of the restaurant.
Fu Lang Mun on Castro Street has a late-night menu--all items $5 or $6 after 9 p.m. It's a steal deal.
My husband just rented a place in Mountain View for his new job. When we were driving down Castro Street, I was surprised to see how many Chinese places were crammed into just a few blocks, although I wondered if they might be more Americanized Chinese. We didn't actually try any, but his new landlords, who are Chinese, said they had dumplings for lunch at Queen's (mentioned above) and that it was very good. Looking forward to checking it out as I love dumplings.
I have to issue a caveat on the pho place, though - the WORST pho I've ever had. When my pho arrived I was occupied with the (tasteless) summer rolls, and I instinctively pushed the bowl away because the smell was bothering me. The broth was awful, I got pho tai and the rare beef was incredibly tough. Pathetic herb plate with just basil, bean sprouts and lime. Ugh.
Cupertino Village is your best bet but in Mountain View itself, skip Castro Street and go to Su Hong Palo Alto (not the Menlo Park one).
The XLB are excellent (all except once where it was super busy and they were oversteamed) and if you get the all chinese menu, there are some excellent choices on it. The sauteed loofa squash with bean curd puff is excellent, there is a braised pork dish with bean curd that's good, along with beef sauteed with yellow chives and bean curd.
I've included the website but the online menu doesn't show any of the all chinese items.
my favorite place for general chinese food is hunan chili in mountain view. they do authentic dishes and some really original ones as well. my favorite dim sum place is in cupertino and is diagonally across the street from the ranch 99 center. TK Noodles is a good and cheap chain for noodle soup, taro and daikon cakes. I lived in Sunnyvale for 17 years and really didn't find any Chinese places there that were great, and went to San Jose, Mountain View and Cupertino for better eats. Hope that helps. Just ask if you would like more specific types of cuisine.