Samples from different camera/lens combos
Usefilm.com has a search engine to show user-submitted sample pictures from different camera/lens/film combinations. Here’s the link for the D70 and the Nikkor 50mm f/1.8D combination.
Unfortunately, they don’t seem to have Sigma or Tamron lens in their Equipment Search dropdown list. I’m leaning towards the Sigma 70-300mm f/4-5.6 APO as the light, cheap carry-around long lens, and I’d like to see some photos. The lens can also be used as a macro lens, with is a bonus.
The sample photos are also somewhat small. I don’t see an obvious link to larger versions of the samples.
PBase.com also has a similar lens sample photo thing, but without the ability to look for combinations with camera bodies. They do have shots from that Sigma, though.