What's your 'Best Buy' Lens?

Just wondering, after reading a few forum posts about different lenses, what is the lens you consider as your 'best buy'? A best buy could be measured by various criteria, e.g. performance vs. price, outright performance, suitability for a specific task and many others.

To start the ball rolling I'll give you mine which is the used Pentax DA 16-45 I bought from a forum member for £140 last year. It's hardly been off my K-5 or K-x; it suits me and my style down to the ground. It's much sharper than the kit lens and I don't miss the extra 10mm at the long end. For sheer VFM and the use I've had from it, this is my 'best buy'.

What is yours?

Regards
David

Sigma 150-500. Pound for pound, they don't come better. Just look at the alternatives at 500mm. Closely followed by Sigma 10-20. I'm either going very long, or very wide, and not much in between

Our best buy was two 18-135mm WR lenses for £295.00 each. They have been hardly off the cameras since.

Used FA35... No question...

Sigma 10-20 - if you measured 'value' or 'best buy' based on price paid divided by number of images taken - I suspect that this lens has cost me less than 5p per image and will end up with a cost of less than 1p per image - it is rarely off the K5!!

sigma24-70 is lens that is most on camera

Sigma 10-20mm or DA 40mm Ltd. Sigma is so versatile and the 40mm is just so tiny and portable with great IQ. Something special about the older M and A lenses as well - penny for penny they are probably my best buys, but I don't use them enough.

Da*50-135mm bought it from the eBay US just as the price increases where announced and a strong pound around 3-4 years ago for the princely sum of £280 delivered and with import taxes etc...

Paid for itself over and over again during that time and my favourite lens...

I once bought a SMCP 135-600mm lens complete with original flight case and close focussing lens for less than £200, a SMCP-FA 50mm 1:2.8 Macro for £100, and a SMCP-FA 135mm for not much more.

Probably the 150-500 for me so far as well. I'm hoping my new 300 DA* will beat it on IQ but will probably not beat its versatility.
In some ways the 55-300 DAL is up there because it doesn't cost a lot but got me on the road to a more successful pathway of wildlife photography.

Tied between the 10-20mm for landscape work or the 43mm for indoor family shots wide open

Pentax smc-A 50mm f1.4 £30
Sigma 24mm f2.8 Super-Wide II £30 (all my successful thunderstorm at night shots taken with this).Both from Wildings before they closed down.
Pentax DA 16-45mm brand new $130 US (last Pentax lens in a shop in Houston when they stopped stocking Pentax)

My best buy was the most expensive lens I ever bought, Pentax 28mm Shift. On film I earned so much money from it, it paid for itself many times over.

Sigma 10-20 and DFA 100mm macro

Like Ken, my best buy is my most expensive lens - the DA* 50-135. The IQ is streets ahead of anything else I own.