I've recently bought a Nikon D300 kit (as you can see from my signature below) and would like to complete the kit with a good macro lens. I've been a very good boy all year and I believe that Santa is scratching his head wondering what to buy me, so I figured I should drop him a hint.
In the past, I've used my old Nikkor 35-105 zoom but I've never been 100% happy with it and of course it isn't the perfect lens to use with a shiny new D300. I'd prefer to stick to Nikon if poss, but will consider independents.
Budget? Santa says £1 for every day that I was good. But wife might disagree!
Sorry I'm a Canon man however nearly all macro lenses tend to be pretty good optical wise. There are some Nikon users at the club so one or two must have a macro lens.
The Sigma 70 and 105mm get good reviews as does the Tamron 90mm, they are cheaper, but not much than the Canon equivalents (likewise probably Nikon) however the outer barrel moves on focusing and they don't have hsm as a rule (faster focusing motors)
The shorter focal lengths around 50mm mean you have to be pretty close for the true macro 1:1, that close that butterflies etc would tend to hop-it before you get the shot. The 90-105 range is a good distance and they are generally f/2.8 for more light. The longer lengths 150+ are good distance wise from your subject, but they are generally f/3.5 and you'll need a shutter speed over 1/200 to avoid camera shake. Ideally for macro the f/2.8 isn't that relevant as depth of field is very limited and you'll be wanting f/16 or more to keep things reasonably sharp. So they are a compromise, like any lens, but they tend to be very sharp.
Thus you need a steady hand or a tripod if going for a larger depth of field. However due to their very good optics they make good portrait lenses, that good that you will probably need to soften the image later to avoid seeing all the nooks and crannies.
There are cheaper options like x2 filter lenses that fit on the filter end of longer zooms, also a 1.4 or 2X tele-converters can get you closer, but you lose infinity focus and some f/ stops, or extension tubes, where likewise you tend to lose infinity focus.
Many thanks for taking the time to reply Phil - it's appreciated. Since posting that request for advice, I've looked at a lot of lenses online and read a whole bunch of reviews. Typically, the lenses which come out the best are those which cost a bloody arm and a leg, so I've decided to hang fire and give my old Nikon 35-105 Macro another chance.
If I find myself really "getting into" macro work, then I can upgrade later.
A proper marque macro lens could well be the best quality lens any of us have.
For most purposes I have found the 100mm ones to be more generally useful. The 50mm lenses are perhaps better for document copying as the working distance is more comfortable, but otherwise it's the 100mm every time.
I have the SMC Pentax-FA 100mm f2.8 and Sue has the more recent SMC Pentax-D FA 100mm f2.8. Both these are stunning lenses, the former being all metal and seriously heavy. The later lens is more compact.
For the Nikon user, I think Nikon still make a 50mm or 60mm Macro, an exceptional lens. Also lenses around 100mm and 200mm. These are all very expensive.
If you get the macro bug, these are the real lenses to have. Expect focusing down to 1:1 (proper macro) so that an object say 1cm long is 1cm long on the "film"
Zoom lenses can focus usefully close (usually 1:4 magnification - 1cm object is 0.25cm on the film) but the field of focus will not be flat and the ultimate quality will not be there.
Next time around we will put a Macro and Close Up workshop in the syllabus, perhaps in the summer.
Thanks guys! Like I said to Phil, I've now decided to make use of my 35-105 from my old F4 kit. I was probably rushing into things when looking for a modern macro lens. Probably better to spend money on a Speedlight to replace my SB-26. It's brilliant with the F4 but is non-TTL with the D300. Mind you, the quality of the lighting using the built-in Auto sensor is still pretty impressive considering its age.
For real macro work manula focus is usually the way to go, so why not also consider the manual focus macro lenses.
The Nikkor 50mm f3.5 is legendary and will out resolve almost any other lens, ever. Current second hand value might be quite low. Worth a look on eBay?
But wife might disagree! 
