Possible lens options (18-200mm type lens)
We should be clear that while 18-200(250,270) range lens has telephoto capability, it is not truly considered a telephoto lens. It is a "super zoom" lens, incorporating wide-angle, normal and telephoto ranges. A standard "telephoto zoom" lens would normally start at 70mm and would extend to 200mm, 300mm or 400mm, with a minimal focal length change due to focusing distance. This an important consideration, if you need "true" 200, 300 or 400mm focal length performance from the lens @ 5-20 feet.
An advantage that truly belongs to the "modern" design of 18-200(250,270) class of lens (from 2004 on) is its ability to focus at 18-inches (0.5 m) (Minimum Focus Distance). A TAMRON SP AF 70-200mm f/2.8 Di LD has an M.F.D. of 37.5 inches (0.95 m). The average 70-200mm, 70-300mm and 70-400mm lens have an M.F.D. of 60-inches (1.5 m) (You simply cannot get a closer focus without some kind of special add-on optical filter).
That being said:
For the A77, which is takes an A-mount lens (which means it is full autofocus available without any need for an adapter, unlike the NEX), a solid choice, for the past several years, has been the TAMRON AF 18-250mm f/3.5-6.3 XR Di-II LD. The lens is a very good version of the 18-200 series... offers a six-year warranty and delivers excellent results for this type of lens at a very reasonable cost.
If you have more money spend, you could opt for the SONY brand of this lens... and if you are really ready to pop some cash, you might find the SONY-mount of the TAMRON 18-270mm F/3.5-6.3 Di II PZD, which is smaller and has the Piezo-electric motor drive. This is a "top drawer" lens and you will pay for this development, where the earlier versions will save money, but are a bit larger, heavier and slower to focus.
That's the options. Good luck with your new lens.
Examining beyond the original question...
Experience has shown that the best plan is to cough up the serious coin and get yourself at least two seriously good zooms for your DSLR/SLT, maybe three. The original posting was an inquiry for the 18-200 "range' lens... which we addressed and suggested the current model, the 18-270 Piezo, which is the best, of course, in that range, Peter.
The choices really were not set up as a debate on whether other range sets would work better, if you broke up the superlens. Of course, that is the better solution and significantly more.
For the APS-C SONY mount, you could investigate:
1) TAMRON's SP AF 17-50mm f/2.8 XR Di-II LD Aspherical (IF)
2) SONY's new 16-50mm f/2.8 DT
for the wider stuff and match it up to a:
1) TAMRON SP AF 70-200mm f/2.8 Di LD (IF)
2) SIGMA 70-200mm f/2.8 EX DG APO OS HSM
3) SONY 70-200mm f/2.8 APO G(D) SSM
to get the upper end.
But if you want some outdoor reach and your not worried about spending a little more... the SONY 70-400mm f/4-5.6 G SSM is the ultimate answer. Nothing listed will disappoint, but just be prepared for a bit of an outlay. It'll be worth it, because your shots will not suffer from stretching these lenses. You'll be covered from zoom to the tomb.