I currently use a machine running Mac OS X 10.6 (Snow Leopard), Core 2 duo 2.0-3.1 GHz processor with 4-6GB RAM. The following is the software I use to compete in the information age:
Statistical & Econometric Analysis: R (primary), Stata, and SAS.
Typesetting: TeXShop (LaTeX editor), with TikZ for diagrams.
Presentations: KeyNote with LaTeXiT
Bibliography organization (& interface with LaTeX): JabRef
Other handy applications useful to the graduate student:
Notational Velocity (synced with Simplenote)