This is the only kind of deal I actually monitor, so I'll keep this thread updated for anyone else interested.
Right now, Barnes and Noble is having their twice-yearly (July and November) 50% off sale! This is generally the cheapest the titles ever get, outside of random Amazon price drops, so this is the time to buy.
Titles I recommend that have been released since the last flash sale:
The sale also applies to preorders that will be out before the sale is over, such as sex, lies, and videotape, and preorders count towards free shipping even though they'll ship separately. I dunno, B&N is weird.
Reminder: You get an extra 10% off in-store with B&N's membership card. Does not work online.
Because of B&N's sale, Amazon has marked down most single-film Blu-Rays to $23, so a bit more than B&N but it might be worth the extra money to not have to deal with them. However, there are some that either match the 50% off or come very close:
BELOW 50% off MSRP (true HOT DEALZ):
Ghost World is also now $17.97 at Amazon.
(Thanks to Josef for the two above!)