Whilst this is a great place to discuss your second armies with your fellow Tau players, sometimes we just don't know enough, or have the same resources that a dedicated forum might have. After all, you wouldn't expect something like Tael's Tau counters on The-Waaagh.com, would you?
So here's a compilation of links to other 40k, fantasy, specialist and non-GW sites that you can learn from to make your non-Tau army stronger.
In addition, it's often a good idea to check out their tactica sections to see what they think their weaknesses are, and any tactics they use against Tau. It all helps.
These are my favourite non-Tau sites below, but please feel free to post yours and I'll add them to this list with your recommendation.40k
(Good Eldar resource, thanks Chronon)http://www.dakkadakka.com/
(great for tourney list tweaking)http://www.librarium-online.com/http://www.wargamerau.com
(Good general Australian site)http://www.warseer.com
(Good for WHFB and rumours too, thanks Eiglepulper)http://www.westgamer.com
(Good West Australian site)
Death Guard: http://www.deathguard.org/
(thanks Afghan Jones)
? (thanks J8).
Space Wolves: http://www.swchq.co.uk
Witch Hunters:http://groups.msn.com/TheEcclesiarchy/ Our own Eltnot's new WH siteWarhammer Fantasy
Beasts of Chaos:http://s2.invisionfree.com/herdstone/in ... howforum=1
Lizardmen:http://z1.invisionfree.com/forums/Thee_ ... /index.php
(Check out my Gnoblog, i'm Ortac)
Wood Elves:http://www.woodelves.org/index.phpBattlefleet Gothichttp://www.battlefleetfury.proboards37.com/index.cgi Lord of the Rings
General LotR sites (thanks Ghost27):http://www.thelastalliance.com/ http://www.one-ring.co.uk/ http://www.thepalantir.org/ Flames of War
(good tactics/army building site)Wargaming in Generalhttp://uk.games-workshop.com/
(best of the official GW sites IMO)http://www.coolminiornot.com
(great painting/modelling site)Role-play gaminghttp://www.thedarkcity.net/