So you got your Canon 5D MarkII or other Canon FF camera and now you want to save some money on lenses. Great, make sure you read this post about the cost/benefits of doing so first. Here is a short list of the best value lenses.
Sigma 12-24mm f/4.5-5.6
If you want to go wide without using a fisheye, this is your only alternative. Very popular for architecture, landscape and street shooters. Be aware that sharpness used to vary a lot in older models (discontinued ones) so you better get new in store.
Tamron AF 28-75mm f/2.8
At a fraction of the cost of the 24-70 from Canon, this lens is a real bargain for such a good performer. Dont let the low price fool you, this lens offers an exceptional value!
Sigma 24-70mm f/2.8
A bit wider than the Tamron version. Get this one, the 12-24 and a 70-200 and you have everything covered in a set of 3 lenses for (almost) the price of a single L glass. Not bad!
Sigma 70-200mm f/2.8
A very good alternative to the Canon model for half the price. Everything on this lens is on par with its competitor except focusing speed and size. So it should be more interesting for videographers than photographers.
Sigma 20mm f/1.8
Cheapest wide prime lens you can get! I really see a lot of use for this lens for videophotographer.
Tamron AF 90mm f/2.8 Macro
Of all the lenses in this list, this one has to be the biggest underdog. Everyone I know who uses this lens is happy about it. It is a very nice alternative to the Canon EF 100mm f/2.8 Macro.
I am sure there are other gems hidden out there. I just reviewed the lenses I have personally played with. If you feel that I missed something, feel free to add it to the comments below!
Andrew Howe suggested the Tamron AF 28-300mm f/3.5-6.3 XR Di LD VC and I have to agree with him. While not as good as the others in terms of image quality, its wide focal range and small form factor make it the perfect travel/walk about lens capable of shooting nice macro as well.