I've had some success using kommandos in the past against Tau. Take a full squad with a power klaw nob and double burnas, you'll be able to hit him hard in the backfield. Adding Boss Snikrot allows you to come on the board exactly where you want and his combined stealth and shrouded special rule will help keep them alive until the following turn when they can charge. Sure they are a target for interceptor, but if you come on correctly, you'll have a pretty sweet save against it. It's actually a good idea to scare him to activate interceptor against such a survivable save because it denies him the use of that weapon his following turn. You can also infiltrate them, but I find the outflank move really forces the Tau player to split their focus, which is brutal for them. Tau need to focus fire on an enemy piece meal and if they start dividing their forces they start to fall flat, except if he brings a riptide wing. But, as Aurics Pride stated, if he does that against orks, by all means slap him.
Koptas are also great against Tau if used properly. If you can turboboost or outflank into his backfield to set up a following turn charge and stay out of harms way until then, you'll devastate his units in close combat. The high toughness of the kopta will allow him to tarpit his unit, especially if you through him against a unti of fire warriors. Add a killsaw and your laughing.
Watch out for overwatch, which can be brutal from Tau. If you can mutli-charge his units with your own, you can direct that overwatch to some cannon fodder or tougher units. Theirs nothing funnier than watching an overconfident opponent thinking that he'll decimate your boyz to overwatch when they charge and you opt to charge some gretchin in first to draw their fire. Sure I may lose have my grots, but now my boyz make it into combat unscathed. with that in mind, gretchin may not be a bad idea for cannon fodder if you have some spare points lying around.
You've got me so jazzed about this upcoming battle, I threw together a little sampler list that I might take. Take from it what you will.
CAD #1 838 points
HQ
Big Mek Shokk Attack Gun w/ammo runt
Troops
Shootas x 11 + Nob w/ big choppa
Trukk w/ big shoota, reinforced ram
Gretchin x10 + runtherd
Elites
Kommandos x9 w/ x2 burna + nob w/ powerklaw
Kommandos x9 w/ x2 burna + nob w/ powerklaw
Snikrot
Fast Attack
Skorcha
Skorcha
Skorcha
Heavy
Lootas x7
CAD #2 661 points
HQ
Big Mek Shokk Attack Gun
Troops
Shootas x 11 + Nob w/ big choppa
Trukk w/ big shoota, reinforced ram
Gretchin x10 + runtherd
Elites
Tankbustas x5
Trukk w/ big shoota, reinforced ram
Tankbustas x5
Trukk w/ big shoota, reinforced ram
Fast Attack
Deffkopta TL-big shoota, buzzsaw
Deffkopta TL-big shoota, buzzsaw
Deffkopta TL-big shoota, buzzsaw
Heavy
Lobba
Lobba
Lobba
Big Meks each join a grot unit and stay on opposite ends on the field, as far away from the enemy with clear lines of sight. Lobbas and lootas do the same. Ensure you space them out enough to ensure an outflanking or deepstriking unit doesn't have a hay day in your backfield. Shoota boyz and tankbustas rush enemy. Ensure you move your full 12" move to reach the enemy quicker. Don't worry about having to snap shoot, its only one less BS than what you already have. The trucks are more distraction than anything. Your primary goal is to outflank with the kommandos and skorchas to burn his backside and sneak in those green baron deffkoptas. Keep him focused one dealing with all your artillery fire and rushing trucks, while he ignores the real pain. Every unit is kept thin on models, forcing him to waste his expensive shooting try to take out single model units. Once you've dealt some pain and split his attention, get into close combat as quickly as possible.
This is an example of a list I've had a lot of success with against gunline armies. Look at it, digest it, cannibalize what you will.