The Neato D5 is on sale at Bed Bath & Beyond for $499. That's $100 off the normal price. Add on a trusty 20% off Bed Bath & Beyond coupon and your total comes to $400 + tax. (BB&B also offers 4% cashback rebates, if you're into that.)
Link: Neato D5
Being at Bed Bath & Beyond makes this deal. The D5 has
been at this price at other places* recently. But Bed Bath & Beyond's return policy is something I wouldn't forgo with one of these.
I strongly prefer Neato over Roomba because of their superior (imo) mapping and navigation abilities. The one knock you'll see on them is long-term reliability. (I suspect it's something that happens with all robot vacuum brands.) I haven't experienced it, but you'll see a lot of reviews claiming problems after the warranty expired. That's where BB&B and their great return policy comes into play. I wouldn't buy these things anywhere else...well, I guess Costco, too, but they don't carry Neato anymore in US stores.
*Why not do a price match? They wouldn't do it since BB&B sells a unique model number.