If you click in my name you will find my trip report on Vn with recommendations for restaurants in Hanoi. Email me if you would like to see my extensive notes.

When will you be in Hanoi, wkwb? We'll be there from January 18-January 22, and in HCMC from January 25-28.

Hanoi-
Ly CLub, near the Sofitel Metropole Hotel, excellent, wonderful service, ate there twice.
Quan An Ngon, a take on food stalls, delicious, casual
Saigon-
Quan An Ngon,same group as in Hanoi but different style, in a colonial home, more formal than in Hanoi, excellent
Xu, hip, modern take on Vietnamese cuisine, wonderful dishes.
Have a drink at the famous rooftop bar at the Rex Hotel

Are you only looking for Vietnamese food, or a variety of international cuisines?

In Hanoi, we enjoyed dinner La Badiane (French, sort of), but it's very pricey for Hanoi.

We loved our lunch at Koto, which introduced us to Bun Cha and Bun Bo, and also to the concept of taking street kids and teaching them cooking and restaurant skills in order to get them off the streets.

In Saigon, we had a very good pizza and salad at La Hostaria, and excellent Indian food at Tandoor.

We actually didn't like the Quan an Ngons very much, but they were certainly cheap and convenient. We met people who ate there every day.

Green tangerine in Hanoi was an attractive and an atmospheric French colonial building right in the old quarter and had a very reasonably priced and good set lunch. We enjoyed it a lot, The menu is on their website http://greentangerinehanoi.com/index.php?lang=en

Also do try some of the Hanoi street food as it is incredibly cheap, amazingly tasty and a fun experience mingling with local families. We found it it very easy to navigate with no Vietnamese language skills just through smiling and using sign language.

Is there are problem with eating the street food? what about water? We are always warned about this as nobody wants the results of impoper sanitation while on a vacation

ladyrep, we experienced no problems on any front with the street food and it was delicious.

I think concerns about this are perhaps over rated the world over and you are really missing out if you don't give it a go in Vietnam. Obviously common sense tells one not to go for anything which looked as if it had been left lying about whether from a street stall or on a hotel buffet but if it is freshly cooked in front of you it is a pretty safe bet. We drank bottled water which was readily available everywhere.

I wasn't so much worried about the food since it was cooked in front of you, but I was concerned about the cleanliness of the utensils and plates. Maybe if you bring your own chopsticks or fork that you can wash back at your hotel.

We ate food from street stalls and small local restaurants extensively in throughout Vietnam without any ill effects whatsoever. Take the usual precautions e.g. Eat at only busy stalls frequented by locals, make sure the food is cooked in front of you and is hot etc. and you should be find. The only time I got sick in Vietnam was eating in the restaurant of a 5* hotel. Don't assume that hygiene standards are an higher in an expensive place, you just can't see what is going on behind the scenes.

As a lot of street food is eaten with hands it is worth carrying a bottle of hand sanitizer for use before and after eating. Sf's comment re byo chopsticks or fork is well made Most Vietnamese will also wash their chopsticks in hot tea before use.. Overall, although there will always be exceptions, we found the food at stalls and in local restaurants to be more authentic, tastier and, of course, a Lo cheaper than in upmarket or tourist orientated restaurants.

As far as water is concerned always drink bottled and make sure when buying that the seal is intact.