• Lighting that doesn't make you feel like your on a supermarket floor.
• Some nice big green plants
• High performance pcs, Dual 22" LCD screens
• A developer wiki
• Sectional dividers so everyone can have their little privacy and not look at each other all day. Avoid cubicles though... there still has to be an interaction environment.
• Ample workspace
• Game room witha pool table/Ping Pong table, nice tv, PS3/XBox/Wii with some multiplayer games.
• A nice kitchen
• Balanced snack/drink machine that caters to healthy and non healthy eaters.
• Nice outside area that is cool in summer where people can sit and relax and eat.

The work is the most important aspect. You can have all these things but still feel like your stuck in a terrible job. Work ahs to feel like fun, and the fun stuff has to be a bonus.