The SIGGRAPH 2011 papers were recently made available in the ACM Digital Library (see here). Although I recommend using Ke-Sen’s excellent papers links page when possible (it links to the freely accessible author copies and often to additional information provided by the authors), not all authors have chosen to make their papers available in this way. The Digital Library itself is pretty expensive (unless you’re a full-time student – see below), but if all you want is the SIGGRAPH stuff (including other conferences sponsored by SIGGRAPH), then a SIGGRAPH membership can get you access. SIGGRAPH memberships are only $42 ($30 for students, but students can get full Digital Library access with an ACM student membership for $42, which looks like a better deal).
In addition, for the first time ACM has published a document which includes the first page of each paper – kind of a paper version of the SIGGRAPH Papers Fast-Forward. This document is freely accessible here, and should be useful for people who just want to skim the papers program and see which papers to read in full. Be warned that the document is a bit large though (184MB). The video preview of the papers program might also be of interest (note that it only covers a few of the papers).
[Eric chiming in: here's the link for how to access the Digital Library if you're a SIGGRAPH member. Note that you can access all issues of ACM TOG as well as all SIGGRAPH-sponsored conference material and journals, not just SIGGRAPH, which is just about everything you'd want for graphics conferences: I3D, HPG, EGSR, NPAR, etc. Also, remember that the cool kids say SIG-GRAPH, not SEE-GRAPH.]