Note: This story contains expired deal information.

If you can plan ahead, there's no reason to pay full price for most Amtrak tickets. Previously, you could enter promotion codes during the payment process on Amtrak.com. You can still do that with some discounts, but most price cuts now require you to book your trip through a dedicated link. Either way, you'll still save 15%–20% on every ticket.

We've found so many Amtrak discounts that we're segmenting them by region. You're likely to find discounts for most popular routes with two gaping exceptions: There aren't many discounts for the east-to-west cross-country routes, and there aren't many discounts specifically for New York City.

Nationwide Amtrak Discounts

Before you start clicking links, make sure to check Amtrak's Weekly Specials, on sale between Tuesday and Friday each week. These are deeply discounted fares (often up to 80% off) that can be for any train in the country. It's a grab bag, but you might get lucky. Check them out here.

There's an ongoing 25% discount (with a 14-day advance purchase) for Northeast Regional trains, the popular line that runs from Boston to D.C. The lower fares automatically turn up when you search, and they're lower than most of the alternatives here. This means the alternatives are better for non-Northeast Regional trains, or for purchases between 3 and 14 days in advance.

Membership has its privileges. If you're a senior citizen, U.S. military, or a member of AAA, Veterans' Advantage, ISIC, Student Advantage, or the National Association of Rail Passengers, you can get a discount on Amtrak fares just by clicking the right box on Amtrak's purchase page. High school juniors and seniors traveling with an adult can get a 50% discount by buying their tickets at www.campusvisit.com. NARP doesn't have any membership requirements beyond the $35 annual fee, and it nets you a 10% discount.

All of these deals have some blackout dates: April 22, 24 and 25, May 27, July 1-2, Sept 2. and 5, Oct. 7, Nov. 22-23, and Nov. 26-28. None of them work with the high-speed Acela Express train. And all of them require you to buy your tickets 3 days in advance, so plan ahead.

New England Amtrak Discounts (ME, MA, VT, RI, CT)

Vermont really wants people to come by train. If you're visiting Vermont from outside the state, book here for 20% off any trip through Oct. 31. But if you're traveling within the state, book here for a flat $12 fare on any in-state trip, through Dec. 31.

If you're traveling on the Downeaster train between Massachusetts, New Hampshire, and Maine northbound in the morning and southbound in the afternoon/evening, you can get two tickets for the price of one by using discount code V773. That's good through July 1, 2011. Up to two children can also ride free on that train with one paying adult if you use discount code V581.

Massachusetts-bound travelers: For any train to Massachusetts (but not trips leaving Massachusetts) on the Downeaster, the Northeast Corridor, or the one daily train from Albany, you can get 20% off by booking here . Good for travel through Dec. 15, 2011.

For trips to/from Rhode Island, save 15% by booking here. Good for travel through Dec. 31, 2011.

For trips to/from Connecticut, save 20% by booking here. Good through March 31, 2011.

Mid-Atlantic Amtrak Discounts (NY, NJ, PA, DE, MD, DC, VA)

Traveling in New York State, or to Montreal? You have two good options. First, try booking with this link, which gets you 20% off any in-state (or Montreal) ticket for travel through May 31. If you're riding the Adirondack train (that's the Montreal train) on a Thursday-Sunday before April 28 and if the resulting fare is higher than $89 round-trip, use this link for an $89 Adirondack round-trip instead.

If you're traveling to/from Philadelphia before July 13, use this link to save 15% off each ticket.

But if you're traveling to/from Philadelphia between July 15 and Dec. 20, use this link to save 30% off a second ticket, which is like saving 15% off each ticket if you travel as a pair.

For 30% off a second ticket to/from Wilmington, DE, book here. Good for travel through Dec. 20, 2011.

For trips to/from Baltimore, MD, get 30% off a second ticket by booking here. Good for travel through Dec. 20, 2011.

For trips to/from BWI Airport, MD, get 30% off a second ticket by booking here. Good for travel through Dec. 20, 2011.

For trips to/from Washington, D.C., get 30% off a second ticket by booking here. Good for travel through Dec. 20, 2011.

Southeast Amtrak Discounts

There aren't many discounts in the Southeast right now, unfortunately. I've seen North Carolina discounts in the past, though, so keep your eyes out for future changes.

For trips to Orlando, Winter Park, and Kissimmee, FL on the Silver Star and Silver Meteor trains, you can get 15% off an adult fare by using discount code V104. Good for travel through Dec. 31, 2011.

Midwest Amtrak Discounts

Note that many of these discounts only cover short-distance trains -- except for the St. Louis link, you can't use them for the long interstate routes.

For trips to or from most Michigan cities on the short-distance Blue Water, Pere Marquette, and Wolverine trains, you can get 15% off by booking here. Good for travel through April 30, 2011.

For trips to or from any city in Illinois on the short-distance Carl Sandburg, Illini, Illinois Zephyr, Lincoln Service, and Saluki trains, you can get 20% off by booking here. Good through April 30, 2011. Note that this won't get you a discount on long-distance trains that don't originate in Illinois or Missouri.

For trips to or from St. Louis, MO on any train, you can get 20% off by booking here. Good for travel through May 2, 2011.

For trips to any city in Missouri on the short-distance Missouri River Runner train, you can get 15% off by booking here. Good for travel through April 30, 2011.

West Coast Amtrak Discounts

The Portland and Seattle versions of the "Chinook Book" coupon book include a 25%-off coupon for Amtrak Cascades trains, which run through Oregon, Washington, and up to Vancouver, B.C. The book costs $20, so it's hard to make that math work if you're just doing it for the Amtrak coupon. But the book has hundreds of coupons for either Portland or Seattle merchants that you might find otherwise helpful.

The East Bay and Silicon Valley, CA versions of the Chinook Book include buy-one-get-one-free coupons for the Capitol Corridor train. The same concerns as above apply; it might make sense if you intend to use more of the local coupons. You can find the full list of coupons at www.chinookbook.net.

For trips to Santa Barbara, Goleta, Carpinteria, Solvang, Buellton, Lompoc, Surf, Guadalupe, and Santa Maria, CA on the Pacific Surfliner or San Joaquin trains, you can get 20% off by clicking here. Good through Dec. 19. 2011.

For trips to Grover Beach, San Luis Obispo, and Paso Robles, CA on the Pacific Surfliner or Coast Starlight trains, you can get 20% off by signing up here. Good for travel through Dec. 31, 2011.

Have you uncovered any other great Amtrak discount codes?