Codex Tau: The Greater Good and You in 6th Edition 40k.

Tau are one of those old codex's that got a substantial boost in playability for 6th edition due to the changes to rapid fire and a couple really good FAQ's. They still suffer high points costs, especially with their vehicles, but they actually became more survivable due to the interaction between a skimmers 5+ Jink cover save when moving, and the Disruption Pods.

Here are some of the cool things with Tau in 6th edition

1. Rail guns. Rail guns remain the best anti-tank weapon in the game (except for possibly the unreliable Zoanthropes Warp Lance). Strength 10, AP1 can wreck any vehicle in the game in one shot, and with the Hammer and Anvil Deployment, you actually get to take advantage of the 72 inch range.
2. Jet Pack Infantry (Crisis Suits, Stealth Suits, and Gun Drone Squadrons) now move 2d6 in the assault phase instead of just 6". While on average this will not make much of a difference in a game, it does mean you can potentially jump forward 6 inches, shoot, and then jump back 12 inches for a net distance gain of 6 inches which is great when fighting assault based armies.
3. Rapid Fire: Pulse Rifles have a 30 inch range and can rapid fire twice up to 15 inches away. This is huge because on average against non fleet foot infantry, they will fail a 9 inch charge more times than they will make it.
4. Hammerhead Tanks: AV13 with a 3+ cover save, this is a Tough nut to crack. Couple that with being able to move 12 inches and still fire that big gun at full effect due to the multi tracker upgrade, your opponent will have a hard time countering these on the field. And with the sub munition round on the rail gun, its deadly against horde infantry as well.
5. Night Fight Experts: Every pure Tau unit in the Codex has access to a Blacksun Filter. These give the model night vision, and you only need 1 model in a unit with night vision to gain the benefits. This lets you take advantage of your superior long range Rail Guns on Turn 1 when you are most likely to have Night Fight where it will matter.
6. Fish of Fury!: Load a Devilfish with 12 Fire Warriors, disembark 15 inches from the enemy, Rapid Fire 24 Str5 AP5 Shots, then either another 7 shots from the Devilfish (with Burst cannon and Smart Missile Upgrade) or Flat Out in front of the Fire Warriors to get some cover and protection from assaults next turn. If you have 2 of these in position, even Terminator squads will melt!
7. Gun Drone Shenanigans: The basic Devilfish comes with 2 gun drones. If you disembark them, they become a small 2 man denial unit that you can possibly take advantage of on the last turn of the game to get a win!