Unless otherwise stated, the below list are for single volume, DVD releases. While yes, you could save money if every volume was available, they often aren't. Such sales are the most useful when you're looking to fill in holes from preexisting collections, or just want to try out an introductory DVD to see what all the fuss is about.
Please (Onegai) Twins
Weather Report Girl
Hell Girl Single Vol. DVDS
Larger Box Sets/Misc.
Utena: Revolutionary Girl Soundtracks (3.99)
La Blue Girl: The Manga 1 ($4.49)
Afro Samurai ($5.38)
Last Exile Flight Pack (Vol. 1-4) ($13.49)
Ouran Host Club, Complete Series (part 1 of 2)($16.18)
School Rumble, Complete 1st Season ($17.10)
Speed Grapher: The Complete Series ($24.28)
Of course, you'll have to do shipping and handling, and even small prices (like 3.59) add up over larger numbers, so buy with caution. That said, there's a number of things I know I'll be buying. Ghost Stories, the wacky liberty taking dub from ADV, is definitely on that list. Also, I want to buy the La Blue Girl manga, just so I can do a serious review on that classic hentai...
limited edition Beck, Vol. 1. For 7 dollars you can get volume one... and an artbox that looks like an amp! Granted, two years after buying it, I've yet to ever watch the DVD, but come on... it looks like a music amp!
Anyhoo, the sale is running through May 3rd, so feel free to check out the entire list for what sales I might have missed. As the list is several hundred deep, I'd recommend getting your reading glasses ready.