Which budget telezoom should I buy?

Is another common theme in most places where Nikon DSLR gear is discussed. Here's my $0.02 on the issue.

First of, my personal favorite:

Nikon 70-300 f/4-5,6G aka the 70-300 g-type
A decent size lens with a usable manual focus ring. You'll read many reviews where it says it's soft past 200mm. Not entirely true, it tends to softness unless you can stop it down a bit. Starting at f7.1 you'll already see major improvements. At the long end it also has some CA problems, especially in contrast rich situations. It does have a very nice bokeh!

There's also a ED version of this lens where one of the element is replaced by an element of ED glass. Supposedly this helps with the CA problems.

70-300G used goes for around 100 euros, a ED can be had for around 150 euros. Here's a close crop of a shot in my flickr album.

Sigma 70-300mm F4-5.6 APO DG MACRO
NOTE! There's also a non-Apo version which is not nearly as nice.

What can I say? It's rather popular due to it's 1:2 macro option. I've handled it a few times and in my opinion the ergonomics aren't as nice as those of the Nikon. I also like the bokeh of the 70-300G more. Those are personal opinions though, this is still a very capable and popular lens.

Can be found used for around 150 euros.

Tamron AF70-300mm F/4-5.6 Di LD Macro 1:2
Well... what can I say? Handled one in the shop once. This is one of those weird lenses where it's hard to find anything wrong but I just couldn't "connect" with it. Optically it's very, very decent as you can see here and in this crop. I did find the macro option, just like the Sigma's, rather cumbersome to focus.

Can be found for very good prices, certainly cheaper than the Sigma, possibly cheaper than the Nikon. Try it in your local shop, if you do find the "click" you'll have a very capable lens for a very good price.

55-200mm lenses:

A lot of salesmen will try to sell you one of these and claim that with the crop factor this will be an adequate focal range. Maybe true but the extra range of the 70-300 can come in handy. Most of these 55-200mm lenses are nice and compact so if you're looking for a telezoom hardly bigger than your kit lens this may be the solution for you.

Tamron 55-200mm F/4-5.6 Di II LD Macro
What a piece of crap! I really, really didn't like it at all! It's lousy at focussing, has bad ergonomics and the results totally failed to impress me.

Sigma 55-200mm F4-5.6 DC
Looks good on paper, never seen it.

Nikon 55-200mm f4-5.6G DX AF-S
This is also sold as part of a dual lens kit with the D50. Really amazing performance for such a tiny little telezoom. Have a look around flickr and you'll see some excellent pics with this lens. I personally didn't buy it because the sample I tested had a rather heavy zoom action. Ended up not buying this lens because I'm so old fashioned that I prefer more bulk to my telezoom, makes it easier to steady it.
If you're in the market for a telezoom and want something compact and/or just don't expect to need the 300mm range I'd seriously advice you to consider this lens.

Second hand lenses:
70-210 f4-5.6 D and non-D: Both good, solid lenses. A D version will go for 160 euros or more thanks to this review. From my own experience it's good but hyped. There's also a 70-210 f4 which is even older. Very slow autfocus but very, very sharp. Can be found for a lot less than the D version.
Then there's a 80-200. Nice retro design, not bad optically but just not a popular range any more.
Another interesting lens on the used market is the 75-240. Due to an unusual tapered design it will take the same filter size as your kit lens, 52mm. Nice compromise, rather light and yet bulky enough to focus properly. Only made for about a year, can be found for good prices used.

Older Sigma lenses: I'd recommend to avoid these. I've had a late 1980s 70-210 which was extremly temperamental and took a lot of effort to procude anything decent. Quality control back then was a BIG problem for sigma. I've seen some very, very good samples and some samples that shouldn't have left the factory. Only consider if you're on a budget and can give the lens a good test drive.