Samsung is planning to launch a pair of monster ultrawide (21:9) monitors later this year which will boast a resolution of 3440 x 1440 and will push refresh rates on that res skywards.
The two planned displays are 30- and 35-inches and will boast a refresh rate of up to 144Hz, thanks to the use of DisplayPort 1.3 tech (previously, this wasn't possible, and if you wanted a resolution at this level, you had to sacrifice that refresh rate).
Of course, there aren't any graphics cards from either of the big players that carry DisplayPort 1.3, which is why these monitors are launching later this year when said video cards are actually on the market.
In terms of the exact timing, OC3D reports that the larger 35-inch model will be out first in Q2 of 2016, with the smaller monitor following in Q3. Both will use a VA panel.
Hopefully we'll see support for AMD's FreeSync on board these ultrawide behemoths, too – there's a fair chance of this, but nothing is confirmed at this point. Indeed, there is no other information currently available about these monitors, but given the release date isn't too far off, it shouldn't be long before we hear more.
Asus is also planning to release a 34-inch QHD resolution ultrawide monitor, the MX34, which has a curved screen and we found to be "absolutely stunning" in our recent hands-on with the display.