Currently, Overstock.com is offering the Mass Effect 3 Collector's Edition (XBox) preorder for $69.20. Coincidentally, group-buy website Eversave (similar to Groupon, Living Social) is offering a(n instantly available) voucher for $20 of Overstock.com credit for the asking price of $10. Using the Eversave deal, which is available for the next two days, you end up shaving an additional $10 off of Overstock's asking price. Unfortunately, they only carry the XBox version of the Collector's Edition, but you can also apply the credit towards any other product on their website, including the Mass Effect 3 standard editions (PC, XBox, PS3), which are ~$55 each.
If you're not interested in the ME3 CE (XBox), the site also offers preorders of Art of the Mass Effect Universe artbook, William Dietz's upcoming Mass Effect novel Deceived, David Gaider's upcoming Dragon Age novel Asunder, and various other BioWare franchise-related books and games.
According to posters at CAG, (1) it is possible to obtain multiple voucher codes if you have multiple email addresses and credit cards, and (2) the vouchers stack with each other, so it is theoretically possible to get $40 of Overstock credit for $20 spent, and so forth.
However, Overstock's customer service can be pretty shoddy at times, I guess they had to cut corners somewhere. So, if you do feel like saving a few bucks with them, pray that everything goes smoothly. Also, if getting something exactly on the release date is important to you, I wouldn't recommend getting it from a website that doesn't guarantee/offer release date delivery.