Below is a running list of some of the sources I've found useful over the years.
Up to half price tickets on the day of performance. Very popular but you must be willing to queue up and have a backup show since tickets can sell out at any time. Also, you will not be able to choose your seating; you will be offered the best available ticket at the time you are at the window. Booths are located in Times Square, Seaport and Downtown Brooklyn. According to a NYT article, go to TKTS Times Square after 5:30PM for the shortest lines and for a list of shows that recently appeared at TKTS, check out this link or download the app.
Check out link at TKTS
Free website membership gives you access to discount codes for a number of Broadway and Off Broadway shows. I like discount codes because you don't have to queue up
Check out link at at Playbill Club Offers
Free website membership gives you access to discount codes for a number of Broadway and Off Broadway shows.
Check out link at Theatermania
Rush, Lottery and SRO Tickets
Depends on the production. Playbill.com provides a nice summary of rush, lottery and standing room only tickets. Also, I like the simple and useful interface at Broadway for Broke People. See blog entry about my adventures at the Mormon Lottery
Check out link at Rushes and Lotteries
Paid membership for certain groups such as students, teachers, retirees, performing arts professionals, unions, etc. Probably one of the best deals in town for the theater. Prices are under $45. Now if you don't belong to one of the groups that qualify for TDF membership, there is a back door. Simply set up a free account at StageGrade, write seven theater reviews and BAM qualify for TDF membership. Check out backdoor details here.
Check out link at TDF
Provides a variety of discounts across the country including Broadway and Off Broadway productions. I typically use it for music events but it is worth checking out for its theater events. Sign up required for free membership
Check out link at Goldstar
Lincoln Center Ticket Booth
Up to half price tickets on the day of performance for Lincoln Center events. Booth is located near Lincoln Center in the David Rubenstein Atrium at 61 West 62nd Street.
Check out link at Atrium
School Theatre Ticket Program
You don't need to be a student to use these discount coupons. I usually pick up any interesting coupons at my local library.
Check out link at Schooltix
Discount codes for Broadway and Off Broadway shows. One cool thing about this site is that no membership is required.
Check out Broadway discounts here and Off Broadway discounts here.
Theater Subscriptions Programs
Subscriptions are typically associated with a particular theatre company. Requires commitment to multiple productions from that company.
Link varies but here is a sample from the Roundabout Theatre Company: Subscription
Audience Extras or Seat Filler Programs
There are a few organizations which specialize in filling seats for a broad range of performances. Generally requires paid membership and a flexible schedule.
Check out links at AE (Audience Extras) and TM (TheaterMania Gold Club) and TE (Theater Extras) and PbP (Play-by-Play). If you are looking for a program with no membership fees but a small ticket reservation fee, check out The Will Call Club at studentrush.org
In my opinion, if you are primarily interested in plays and musicals, then TheaterMania Gold Club is the best of the bunch.
If you would like to purchase a discount ticket directly from your smart phone then TodayTix may be for you. It has an easy to use interface and they deliver the tickets to you outside the theater. I notice that on a limited basis they have lotteries for certain shows (e.g., On the Town). Also, some users post a first time purchase discount code on the BroadwayWorld Message Board. I don't know if they work, but it is worth a shot.
For more information about TodayTix, check out link here.
Theater and other discounts are available, if your company is a member of their employee discount program. I like Working Advantage for harder to find discount tickets such as The Lion King and Jersey Boys. Check out link at Working Advantage.
Similar to Working Advantage, theater discounts are available if your company is a member. Check out link at Plum Benefits.
Similar to Working Advantage, theater discounts are available if your company is a member. Check out line here
Met Opera Rush Tickets
A limited number of seats are available on weekdays ($20) and an online lottery is available for weekend performances ($25). A great affordable way to see the opera.
Check out link at Met Rush Tickets
Special Off Broadway promotion during the month of February (a slow month for theatergoing) and other months as advertised. Tickets are only $20 at the box office 20 minutes before the performance.
Check out link at 20at20
Signature Theatre Company
Signature Theatre Company has committed over the next decade to making the theater accessible to all audiences with $25 tickets. I absolutely love this theater company.
Check out more details here.
Access Roundabout - HIPTIX and $10 Previews
The Roundabout Theatre Company offers $20 tickets to young theatergoers age 18-35 through their HIPTIX program. For those like me who don't quality for HIPTIX and don't mind checking out the first 4 previews of a new show, use code "ACCESS10" to purchase $10 preview tickets.
Student and Youth Program Discounts
I started going to the theater on my own in high school and was always appreciative of all the discounts available to young people. Here are a few programs catering to our future: High 5, student rush tickets (Broadway list / Off Broadway list), and Schooltix. Every so often, even at my age, I like to check out BroadwayForBrokePeople.com.
The Broadway Meetup Group
If you are the social type, definitely check out The Broadway Meetup Group and take advantage of the group sale discount.
Check out more details here.
I am not necessarily encouraging it but if you would like to use your precious air miles for free theater tickets, you can do so through Audience Rewards.
Social Media Sites
I've noticed an increased amount of free and promotion tickets on Twitter and Facebook. If you really want to see a show, check out these social media sites and you may win free or discounted tickets. For ease, I've created a Broadway Twitter List. Feel free to subscribe here.
Volunteer as an Usher
Many Off Broadway and smaller theaters have volunteer usher programs. Check out the theater website for the show that you want to see for more details.
Deal and Flash Sale Sites
Deal and flash sale sites have grown in recent years. Increasingly, theater tickets are featured on these sites. For example, check out Groupon and Gilt New York City.