There are frequent buses from Quito.
Most buses make their final stop in Tulcan's bus station. It's small, but there are taxis and restaurants around and open even on Saturday nights. Hotel/Restaurant Acacias is across the street.
Unfortunately the taxis have fixed the price to and from the border into town at $3/trip, even though this is more than it should be (or would be if they had meters).
There's a place called Hotel Las Acacias just across the street from the bus stop which has clean comfy rooms with hostel prices and you save money by not having to get a taxi to another place. There's WIFI, but only in reception or in rooms close to it, we stayed in the room directly above and had a good WIFI signal, but also had constant noise and light from the street. Good for a stopover before doing the crossing and journey to Popoyan/Bogota/Medellin in the morning which is apparently much safer than doing it at night as that particular stretch of road is "dodgy." There are also another couple of places to stay right next to Acacias, but I didn't stay in them so can't give an opinion...
Ipiales is just on the other side of the border and can be reached with collectivos or taxis.
Take a taxi to Rumichaca bridge. $3 (8/2014). Walk across the bridge, taking care of formalities with Ecuadorian and Colombian officials.