it all depends on the car. models with fewer options leave less room for the dealer to profit and are accordingly harder to talk them down on. I spoke to about 10-15 dealers (via email) in the new england area over the last 3 weeks. Only one (the biggest) was willing to go below significantly below invoice, I was able to talk most of them down to invoice though. Mine is a base, WR Blue hatch. I ended up getting mine for $400 under invoice, but that felt like an amazing deal.
Invoice would be a very good deal. Anything over invoice + $200 would be a better deal for the dealer than you.
This is, of course, for a base model. If yours is optioned out then you should be able to get more off. Also, don't forget about doc fees. What dealers lose in the negotiation process they often make back in doc fees