In reply to Andy Hudson:
I guess ultimately it depends on exactly what you're using it for. A few thoughts on the lenses I own and use everyday:
14-24, F2.8 - Probably one of the best 'milky way' lenses with little coma at 14mm. 14 is very wide though even for landscapes and it doesn't take filters.
16-35, F4 - Excellent value for money. Very sharp, takes 77mm filters though does have a decent bit of distortion at 16mm.
24-70 F2.8 - Superb general use lens for landscapes and portraits. I find myself using this more and more for landscapes as wide angles manage to make even huge peaks look very small unless you're stood directly under them. The new 24-70VR is no sharper, heavier, bigger and more expensive. I'd second Icnobles suggestion of finding the non VR version second hand if you're thinking of this one. Unless of course you're planning on doing a lot of hand held shooting in low light.
80-400 F4.5-5.6 - Not as sharp as a pro prime zoom (I'm thinking of investing in the 300 2.8) but it's exceptionally convenient with such a big zoom range.
28-300 - F3.5-5.6 - I use this if I'm going on holiday / travelling light and I'm not sure what lens I need. It's obviously not as sharp as the above lenses with such a huge zoom range, but it's small, light, sharp once stopped down and exceptionally convenient.
As others have suggested I'd put your money in lenses not bodies. A good lens will last many years and doesn't really loose much value (if you go pro the lenses actually gain value with inflation). The D810 excellent though it is will be well and truly out of date in 5 years. The Nikon 24-70 2.8 is my go to lens and was released in 2007. I'll likely keep using it for another few years yet.
As far as 3rd party lenses go the Sigma Art series are attracting a lot of attention. The Samyang 14mm 2.8 is hard to beat price wise for astrophotography.
I hope that helps a little!
Some work at:
https://jamesrushforth.smugmug.com/Portfolio/ (If you click the information button on an image you can see the lens used and exif data if that helps with decisions).