I'm doing a Galapagos tour in May, and have five days afterwards to see the rest of Ecuador. I'm skipping the Amazon because it warrants a trip of it's own. Other than that, I'm open. I've done loads of research, but am now overwhelmed by the options. Cotopaxi, Mindo, whitewater rafting, devil's nose train are all topping my list right now, but would love to have some opinons... I genereally stay away from tourist-y places, so was going to avoid Otavalo and Middle Earth, but could put them back in if necessary.
I thoroughly enjoyed Mitad del Mundo (middle of the earth). Went on a Sunday, which is when many people from Quito go. Yeah, there were some gringos, but it's a fun place with loads of museums and interesting things you can't do anywhere else. But the most enjoyable thing for me was being somewhere where Ecuadorians take a day off, and being among them.
I can't speak about any nearby things to do; Quito was my R&R after a month living on a jungle farm. I didn't do much but vegitate while I was there.
I also enjoyed Mitad del Mundo but you could also take a bus down to Banos, a lovely little town with hot springs and a volcano, you can go rafting, horse riding etc. Having said that, Quito itself is lovely and you could probably quite easily spend 5 days immersing yourself there. Check out the South American Explorers Club, they have a place in Quito which is awash with all the latest info, have a great library and you can even leave your luggage there.
Not been myself but Mindo looks pretty cool!