Because I'm compulsive and like to get the best deal possible, I've been researching completion discounts. These are the ones I've found so far and thought I'd share for brides who are still undecided about where to register. Please feel free to add if I didn't list one you're aware of:
Amazon: No completion discount, but guests with Amazon credit cards get 3% back on purchases made through Amazon.com. Free shipping on most items over $25. 4-for-3 discounts on many homeware items including formal china, flatware, and crystal... which can be up to a 25% discount for 4 items of the same value.
Bed Bath & Beyond: 10% off what's left on your registry; some select stores do 20% off completion parties for anything in their store several times a year.
Belk: Receive a $25 off a $75 or $100 purchase for registering in-store; 10% off completion discount post-wedding, with two 20% off completion events during the year, with few brand exclusions.
Bloomingdale's: 10% off completion discount post-wedding; 20% off first anniversary "gift" for items remaining on your registry; 20% off friends and family event (unclear what this is, but they do advertise a separate 20% off coupon for your first anniversary).
Crate & Barrel: 10% off completion discount for ANYTHING you add to your registry up to 6 months after your wedding... so you don't have to embarrass yourself by asking for that $1000 cabinet you were planning on buying with the discount during a time when guets are likely to see it.
Dillard's: 20% off completion discount on remaining registry items for 3 months after your wedding date.
JC Penney's: 15% off completion discount on remaining regitsry items for 3 months after your wedding date.
Kohl's: Probably the BEST of all of these: 15% off completion discount for you; 15% off for your guests with a coupon they provide (though it may break etiquette to distribute these coupons widely to guests - could be useful for some VIPs); a voucher for 10% of what guests spent on your regitsry, up to $200 (so it counts for what guests spend up to $2000).
Macy's: 10% off completion discount for items remaining on your registry post-wedding. If you have a Macy's credit card you get a gift card after your wedding date (assuming your credit card is in good standing) that is equal to 10% of everything you spent from the time you enrolled in their star rewards program and 5% of everything your guests spent on your registry. Macy's advertises that the average gift card amount is $100.
Pottery Barn: Same as Crate & Barrel - 10% off anything added to your registry for 6 months after your wedding date. The PB credit card also gives you 10% back in rewards for purchases made at PB, which may be useful if you plan to complete expensive things there like furniture or bedding.
Sur La Table: 10% off completion discount for the entire store post-wedding for 6 months. They also allow you to make your registry completely private, so guests won't see if there are a few high-end items you want to buy on your own with a discount afterwards.
Williams Sonoma: Like CB and PB, 10% off anything left on your registry or anything you add to your registry post-wedding for 6 months. If you open a Williams Sonoma credit card, you get a $25 gift card, free shipping for the year, and 3% back on what you spend at WS. If you link your credit card to your registry you also get 3% back on what OTHER people spend on your registry, like Macy's and Kohl's.