About 2 years ago
Climbing Cotopaxi (5897masl and about 2 hours south of Quito) might possibly provide the best view in the whole of Ecuador. It's not a trip for the fainthearted or unfit and involves a climb of approximately 1000m from the last refuge - most of this is through snow. Unless you are well aclimitised you should allow at least a couple of days to get used to the altitude.
There are quite a few tour companies providing guides and I went with a group called Cotopaxi Cara Sur (they have an office in Quito and Eduardo the owner will meet you before you go). They provide all equipment including boots, crampons and an ice axe. They also own the only refuge on the south side of the volcano. I would recommend these guys because they got me to the summit safely on a tough day when nobody else reached the top.
This trip is so worth it. After 6 months in South America it's still in my top 3 experiences.