Some of the papers I have worked on have been influential (e.g., Maciel's I3D one) but most of these are superceded by improvements in subsequent papers, or are mainly of theoretical interest. Here is my current list of the most useful papers that are also easy to implement. I will include Mike Stark's b-spline paper as soon as I find an online copy. Note I will not post a list of papers that were a dumb idea! And also for you new people in the field, take note that half of these were rejected the first time, so never assume the reviewers know what they are talking about (or that they don't! Just read reviews with a scientist's skepticism).
A Ray Tracing Framework for Global Illumination, GI 91. This paper repeats much of Arvo and Kirk's metahierarchy work which unfortunately I wasn't aware of at the time, but also spells out how to manage the various abstract classes in a distribution ray tracer. It also includes a better way to sample the disk, later spelled out in a jgt paper. Most of this stuff is now standard practice, but good if you are new to the field.
Direct Lighting Calculation by Monte Carlo Integration EGRW 91. This paper lays out what to do when you have
more than one light. The follow-on TOG 96 article has some more details, but except for the light grid I think most of them are not worth the added complexity. I do think there has been little subsequent progress on the "thousands of lights" problem which is a shame, but the Cornell folks have recently been doing lots of interesting work on it.
A Practitioners’ Assessment of Light Reflection Models . Pacific Graphics 97. Section 5.1 is especially useful. If you have a bump or displacement map, you really only need a BRDF for the subsurface part, and this one is as simple as they get.
The irradiance volume, CG&A 97. I think that like ambient occlusion this technique has tons of problems but in practice is "good enough".
A Non-Photorealistic Lighting Model For Automatic Technical Illustration, SIG 02. Section 4.2 has all you need to know. Simple hack, seems to work.
Interactive Ray Tracing for Isosurface Rendering, Viz 98. This just plain works. Steve Parker's group still uses the same technique and it shows no signs of losing its utility as it scales so well.
An Anisotropic Phong BRDF Model, JGT 00. This works surprisingly well in practice. It is no good for cloth though-- I would love to see a similar model for cloth.
A Spatial Post-Processing Algorithm for Images of Night Scenes, JGT 02. This still needs to be extended to animation.
Photographic Tone Reproduction for Computer Graphics, SIGGRAPH 02. The first simple model works well on almost all images I have seen. Erik Reinhard et al.'s book is definitely worth picking up for putting this model in context.
An efficient and robust ray-box intersection algorithm. There is also source code at the JGT site. This paper made me hate IEEE FP because of negative and positive zero.
Optimizing Ray-Triangle Intersection via Automated Search, RT06. This is really just Moller-Trumbore 2. I was shocked that the automated search actually worked, and unsurprised the subsequent hand tuning did too.
Image Synthesis Using Adjoint Photons. Graphics Interface 06. This paper is how I now think about path tracing, and it maps directly into some pretty sweet code. The author list is long but Boulos and Morley are really the two principle guys behind it. It takes advantage of the same properties of light as the dual photography paper. Jared Johnson, Solomon Boulos, Austin Robison and I have extended this to linearly polarized light which we will write up soon. I am hoping that a clean extension to fluorescence is also possible.
Ray Tracing Deformable Scenes using Dynamic Bounding Volume Hierarchies, ACM TOG 07. I have been advocating the BVH for years-- maybe I am just too lazy to really learn k-d trees. But the real advantage of BVH in my opinion is dynamic scenes. Note that the presentation of the packet-culling is a bit weak. For more details see this tech report.