Well, this is my own personal opinion so don't start screaming at me claiming that I'm wrong. I may be.
Firstly, Taric. I won't really call him a support character, but he works pretty well that way. Some tips:
Get Phage/Frozen Mallet/TriForce (I go for Frozen). This helps your team gank more effectively. Alternatively, you could go for the Lizard Buff, which works really well.
If your team have champions going for mass health or champions with low tanking ability, you could try for Aegis of the Legion. It helps with staying alive as a team and improves damage somewhat. Stacked with Shatter, its epic.
Getting Mercury Threads is really useful against casters. It makes their disables much less effective and give you some Magic Resistance.
You could try for Thorn Mail/ Warden's Mail, should you be fighting against a dps.
Starting with Mana Manipulator whilst laning with a nuker makes life a lot easier.
When facing a ranged enemy, run into a bush. If they choose to go for you, hit Dazzle and wait for them to come closer. When they do, just cast it and Shatter. This should rip a chunk of health from them and give you a huge edge in killing them. Even better if there's a way to slow the enemy, since you can throw in another Dazzle to finish it.
Generally, I don't choose to level Imbue early game. However, you could level it instead of either Dazzle or Shatter.
Next, lets discuss Anivia.
I don't really play her, so I am unable to say much. However, 1 level of that Crystal Wall thing is really helpful when chasing/running away.
Zilean is really good at supporting. What I would suggest is:
Max out Time Bomb.
Put 1 level of Rewind at level 2, then max out Time Warp. Level Rewind at later levels.
Level Ultimate whenever possible.
Like many other supports, pick up a Mana Manipulator. Go with a champion that may suffer from Mana Starvation (Cho'gath is a good example). Just use Time Bomb to harrass the enemy and control the lane. Generally, you should plant it on an enemy champion. Althernatively, you could plant it on a minion that a champion is set out to kill. The bomb will blow and damage the champion(s)
Whenever possible, get away from your lane and gank another. Make sure you mark out the champion, preferably one that's easy to gank. The process is rather simple, it goes something lilke:
Make sure your allies start attacking. Time Warp the enemy and set a Time bomb. Immediately Rewind and set another bomb. Rewind may not have been refreshed yet, so just attack them. If they run beyond the turret with your time bomb, don't chase and just pray it kills xD.
Ultimate is straightforward. Use it on your team's main DPS or the one getting gank/targetted when they are near death. Use it on yourself if they aim you before anyone else. Straight after, throw in your bombs and warps.
Innervating Locket, Abyssal Scepter and other AP/slow/Mana items work wonderfully, especially if you choose to get Archangel Scepter. Pick your boots based on the situation.
I don't play Janna, so I don't know what to say :P
Karthus also works rather well as a semi-support. Wall of Pain is probably the best ganking ability against more than 1 enemy. I mean seriously, 80% slow with 35 magic resist/armour reduction? That's plain sick. If you go for Rylai, it also helps you slow the enemies even when you don't have Wall of Pain. Spamming Lay Waste and Defile (a note about defile, when you activate it, it can slow every enemy only once, the only way to slow them again is by deactivating defile and activating it again).
There is a general rule about support champions:
Don't go in without your core support skill. Chances are, you will fail.
For Anivia, make sure you have enough mana. Same with every other champion :P
Zilean should have all his spells ready. That's the best option. Otherwise, everything other than Ultimate is good enough.
Have fun LoLing