I’ve lately found some same-day cheap airfares to various U.S. cities, so I’ve experimented with doing day trips by air. (They’re not strict mileage runs since I actually leave the airport, unlike a true MRer.)
So, a few cities where getting from the airport to an interesting part of town doesn’t take a car, more than $2, or more than half an hour:
* Austin: A cheap ride direct to downtown and campus, although I didn’t think it very walkable once off the bus.
* Boston: We’ll see how this goes next week, but I’m going to try the Silver Line instead of the Blue + shuttle, and maybe see how the North End and/or South Boston Piers have changed since the Dig.
* Chicago: From Midway, try the South Loop; from O’Hare, try Wicker Park.
* Los Angeles: A fairly frequent LAX shuttle bus runs to the LAX Transit Center, but don’t bother with LA; instead, explore nearby Venice and Santa Monica with the Big Blue Bus. (The FlyAway to Union Station works well enough, but could take a while.)
* Minneapolis: The train runs to either downtown or the megamall (and Ikea!). To get to Uptown, transfer to a westbound 21 bus at Lake or go downtown (passing the new riverfront area) and take a #6 bus headed down Hennepin, which also swings by Loring Park and the Walker.
* Portland: MAX runs directly to the eminently walkable downtown.
* Queens: The Q33 is a short ride into Jackson Heights from LGA, and from there the #7 goes to Flushing.
* Washington: Perhaps the easiest anywhere: fast and efficient Metrorail stops right at National.
* Two I haven’t tried, but which have rail to the airport: Cleveland and St. Louis.
A sidebar: one-day ski trips on transit. I only know of three ski slopes with 7-day public transit access from a major city, although I’d certainly love to know about others:
* Eldora Mountain near Boulder, Colo.: RTD bus N from the Boulder bus station
* Grouse Mountain in North Vancouver, B.C.: Coast Mountain bus 236 [pdf] from Lonsdale Quay
* Snowbird/Alta, along UTA’s Route 998 out of Salt Lake City. Only two buses a day, though.
* Special mentions go to the Winter Park Ski Train, Amtrak’s Vermonter, and the proposed Québec-Le Massif train although these aren’t transit buses. Many other resorts run private motorcoaches within town or to nearby airports or cities.
Additional special mentions go to Santa Barbara Car-Free, which promotes car-free trips to Santa Barbara, Calif., and CATCO’s Going to the Mountains from Calgary. CATCO’s slogan, courtesy Bill Ford: ‘If you live in a city, you don’t need to own a car.’
west north 
posted at FlyerTalk about transit in LA.
Transit and city form are a chicken-and-egg problem: without good transit, things (houses, offices, tourist attractions) will scatter all over the map, which makes it difficult and expensive to provide good transit. Put simply, perhaps it’s not because the train doesn’t go there, perhaps it’s because the “there” doesn’t go to the train.
“Who Framed Roger Rabbit?” is obviously a dramatization, but it has some basis in reality: the initial sprawl of Los Angeles was driven by streetcars, not automobiles, and even today many of the freeways follow old Pacific Electric routes. Enough of that old “things clustered around old transit lines” infrastructure remains to make at least a limited view of Los Angeles possible without a car: Wilshire or Santa Monica boulevards through the Westside, for instance, are pretty obviously lined with cool things to do. That might be why it’s the focus of a few Transit Adventures itineraries from Experience LA (the local tourist board). Similarly, UAL’s in-flight magazine recently ran a feature article on LA by Metrorail.
There’s also this NYT piece on Santa Monica and Venice largely without a car. The Big Blue Bus heads from LAX’s bus terminal right through Venice and into SM.