xD Spint, congrats on firsting the Thaumaturge forum.

To answer your question, Conjurer is an excellent complement for Thaumaturge all the way through to rank fifty. First of all you get your party buffs (Protect, Shell, Stoneskin, Shock Spikes) as well as a second Cure. You get the second tier of elemental nukes at 24. Sleep, learned at CON32, is a pretty big one, it goes great with Thaumaturge's AoE for nice crowd control. Profundity II at rank 34 is great for your nukes, you can also use it with your Shadowfall for a nice instant area of effect damage with no cooldown. At rank 38 you get Raise, it's pretty nice to have both Resurrect and Raise on hand for when they're needed. The real gem I think is Chainspell at CON40, best used with Resurrect/Raise or Shadowsear. 42 is the second tier of Shock Spikes and Stoneskin. Then you get the final tiers of Protect and Shell and Cure at 48.

As far as other classes go, I find the survival skill to be quite useful. If you're taking hits, you can use Featherfoot (PUG12) and Foresight (MRD12) and maybe some of Gladiator or Marauder's fancy defense abilities like Rampart or Defender to avoid some damage.

Other classes offer traits which are purchasable through guild marks that are useful for all classes, not just Thaumaturge. Such traits include, but may not be limited to, Fleet of Foot (Lancer), Out of Sight (Archer), Fast Cast (Conjurer), and Prime Conditioning (Pugilist).