Why did Gandalf have a ring?

[Boromir88]

Cirdan was the original bearer of Narya. But when Gandalf came over from the West, Cirdan had better forsight than any one else on Middle-earth. He foresaw that Gandalf would (of the other wizards sent) stay true to his task and he would be in need of Narya:

...For Cirdan saw further and deeper than any other in Middle-earth, and he welcomed Mithrandir at the Grey Havens, knowing whence he came and whither he would return.
"Take this ring, Master," he said, "for your labours will be heavy, but it will support you in the weariness that you have taken upon yourself. For this is the Ring of Fire, and with it you may rekindle the hearts in a world that grows chil. But as for me, my heart is with the Sea, and I will dwell here by the grey shores until the last ship sails. I will await you."~Appendix B

Cirdan saw that Gandalf could use Narya, and since he was going to stay the rest of the time in his dwelling, The Grey Havens, he would not need the Ring. Being the nice elf, he gave it to someone who could use it.

And a very belated welcome to the downs.