I like to play a disruptive "capture" style game. Constantly moving between undefended enemy points and at least trying to disable or better yet capture the points if able. It's a great disruption tactic, because you force the enemy to have to constantly shift their focus between trying to cap and defend against you. In this role, I have been having tremendous success with Soraka, Sivir, Alistar and especially Janna. However, I think you could pretty much adapt it to any character.
1) Boots of Mobility - Makes you fast
2) Priscilla's Blessing - A temp speed boost and increased capture rate
3) Ether Rylai's Scepter or Frozen Mallet - Health & ether more attack speed and damage or ability power. However, the slow effect is really the important aspect here.
Seriously, these are the only items you need to play this way. I usually don't even bother heading back to base to buy more stuff past this point unless I die.
Runes: With Sivir I use a rune page that is +Damage, +Armour Pen, +Attack Speed, +Health
With Janna, Alistar and Soraka i use CD Reduction, Armour, +Health, (I think that's it)
Masteries: for all but Sivir I run 9/0/21. Sivir is 25/5/0.
Janna I think is the queen of capture. She is SO fast on her own. When you add the Mobility boots into the mix combined with her passive and the movement speed boost from Zephyr she has to be the fastest champ in the game. Add Ghost walk and Exhaust to your kit, and you should be able to out run anyone. Your first 3 points should be spent 2 on Zephyr and 1 on The tornado. Rush the windmill with your ghost and be sure to grab the speed boost in the jungle on your way. You should be the first person at the tower. Use your tornado to delay any enemies that arrive before the rest of your team. Once your back up arrives here is where the fun begins. If the fight at Windmill is still going on, let your teammates carry on the fight and slip out the back and head to one of the enemies points and start back capping. Go for the disable and cap if possible, but be prepared to bolt should anyone challenge you. From here on out just keep moving about the map back capping any point that is left undefended. Janna has enough skills in her kit that are effective at displacing enemies trying to chase you that you should almost never get caught.
I use this same tactic with the other characters, and it generally works pretty well.