I have a friend who is visiting SF for a week and I've been going through a list of things he must see while there. He'll have access to a car and so I'm thinking about the Greater Bay Area as well. Some highlights so far:

1) Burritos in the Mission. Everyone has their favorite but I'd go with either El Toro or Pancho Villa. Buy the super burrito and hang out in Mission Dolores Park. It's one of the things that made me fall in love with SF.

2) Dim Sum at Yank Sing. Definitely have the soup dumplings. And everything else.

3) Bike/hike through Golden Gate park to the ocean. Don't miss the Bison Paddock.

4) Take the audio tour on Alcatraz. Obviously very touristy but even locals admit it's amazing (when they go after 10 years.)

I have honestly been to Alcatraz 6 times and totally love it. It is definitely the best tour I have ever been on.

Also eat at yelp.com and make sure to get the imperial roles

This is a bit difficult because I don't know your friend and their interests. My universal list for folks of things that haven't been mentioned:

1. Golden Gate bridge. I always take people to the Golden Gate bridge and the recreation area above it. It's great for pictures. It's a natural segway into driving through Sausalito and parts of Marin.
2. House of Nanking. If you really like Chinese food, I highly recommend that people do this.
3. Ferry across the bay. I'm really partial to taking a ferry from SF to Sausalito or Tiburon. It's a really good time and this time of the year the weather is likely to be warm during the day.
4. SF Giants game. Even if you don't like baseball, ATT Park is stunningly beautiful.

The Giants game idea is great. Anyone with a passing interest in sports will enjoy AT&T Park. It probably is the best modern ballpark.

What about outside of SF proper. Oakland tips? Marin?

One that I do with visitors quite often is drive across the Golden Gate bridge, stop at the vista point right on the other side. And the take the drive up the Marin Headlands. The road has been recently repaved and there are many spots to pull off and admire the view back into SF. Also it's great to stop at all the abandoned artillery batteries and wander around there.

For outside of SF, I think it really depends on interests. A couple of other suggestions
1. Napa/Sonoma - Whether you like wine or not, it's truly beautiful and you can have a great time really cheaply by just driving to the wineries and walking around the grounds.
2. East Bay - If you're into outdoor activities like hiking or nature walks, the East Bay hills are a really nice place to do it. The one problem with that now is that they get very hot in August, so it might not be the best time to go.

I haven't eaten it in years but the focaccia at ilfornaio.com is really great.

If they're biking through GG Park, they should consider stopping by either the Cal Academy of Sciences, the Japanese Tea Garden, or the De Young museum which has an amazing (free) view of the city.

I didn't know the view from the top of the De Young was free admission. Noted!

On the not-as-cheap list: My favorite ...
* italian: Perbacco
* steak: Bourbon
* sushi: Kiji
* brunch: Starbelly
* thai: Osha (Marnee is also good)
* indian: Amber (Bombay is the cheap alternate)
* meal: Zuni (roast chicken for two, start with the oysters)

Also Ian is a troll for recommending Tu Lan:

sfgate.com

"Health department inspectors found that Tu Lan, the famous and sometimes infamous establishment nestled in the gritty Sixth Street neighborhood south of Market Street, stored food at improper temperatures, didn't have proper hand-washing stations, was crawling with cockroaches and mice and wasn't bleaching its cleaning cloths."

Delicious!

Oh man, Perbacco and Barbacco are so good. House of Nanking is also great, especially if you just give the waiter instructions to bring you a couple meat/veg dishes they like. I think my main SF tip would be to walk around as many different neighbourhoods as you can: the standard places (Pac Hghts, Castro, Chinatown), but also places like Clement Street in the Richmond. For East Bay options, the Gourmet Ghetto in Berk and Temescal in Oak both have a lot of great food. I also really like the Off the Grid event on Fridays at Fort Mason, where they get ~30 trucks/carts together and have live music and beers. Gets cold, though.

Clement Street: lunch at Giorgio's Pizzeria, get a dessert crepe at Genki, browse the bookshelves at Green Apple. there are tons of cutesy shops now.