Would have to agree that the 8800GTX and 8800GT have still been the most influential cards of the last few years even though almost a decade old.
The leap in performance and feasibility of many shader effects that previously either weren't possible or not possible with decent performance pushed rendering tech forward more than anything since and the impact of those cards is only really starting to fade away in the last couple of years or so.
Following on from that the GTX480 due to making tessellation feasible - while not a big fan of tessellation myself and its not been overly used itself it seemed to be the catalyst for developers pushing related/newer tech.
The 290 influencing the 780 price drop is another valid one in there.
Overall though I don't think we've really seen hugely influential cards over the last few years - the Titan had a bit of an impact on multi display gaming due to the sudden leap in what was viable performance wise with multi display/high resolutions but rendering tech wise not so much as it was in some ways an anomaly and developers wouldn't focus on it at the expense of more mainstream cards in that regard.
While theres nothing to confirm it - "leaked" "7870" slides (which are almost certainly real) had the 7970 specs and projected release date on them. (Before the actual releases).
If you look at how Amd have been in the market you can see things. Essentially the biggest proof to Amd's marketing, releasing with lower clocks than needed. Never have Amd released a gcard with so much overclocking headroom.
Waiting purposely 6 months then magically offering a bios upgrade to hit 1ghz, (for people who can't overclock)
Then at same time ghz edition cards were made. Were the initial lower clocks, to extend their own product lifetime knowing 28nm was hard to make at full fat, or to help Nvidia market their own mid range offerings?
6 months from that we then see the famous cat 12, drivers,
So after almost 1 year exactly we now see the full potential of the 7970, although prior to driver update, if you weren't blinded by reviews at stock speeds (925/1ghz+ boost) and you did your own overclocking at 1150mhz plus, you could still beat a 670/680 with overclocking but some games the 680 still had the edge.
Then for 2013 well we all know about the 8800 oem rebrand year, pretty similar to 2014 rebrand year,
But of course Amd were experiementing with gcn 1.1.
Experimenting with Bonaire, 7790 etc .