Avianca is a Colombian airline that offers flights around Latin America, the U.S and a few destinations in Spain. I flew with them on two return flights, once within Colombia and once from Quito to Caracas. Avianca has the broadest connections for the northern half of South America of any airline.
Flights in South America are rarely cheap and as far as I am aware there is no budget airline that would match the likes of ryanair or easyjet within Europe, however, Avianca does offer reasonable value for money. Their flights are frequently the cheapest that I could find for travel around the Andean and Caribbean region.
The airline is not very useful to get from Europe over to the Americas as it's only connections are to Madrid and Barcelona. Prices are on par with any other trans-atlantic flight.
The flights themselves were excellent with comfortable chairs, standard leg room and very clean and well-maintained. There was also in-flight entertainment with communual TVs showing films and TV-all in Spanish or dubbed. I'm told that on longer flights all seats have their own TV with individual control although can't verify that. They also provided plenty of newspapers and magazines although again all in Spanish.
Staff were friendly and attentive and all spoke English very well (I even had to ask them to speak in Spanish!). They provided a snack and drink on all flights.
All Avianca flights use E tickets (website avianca.com, can be viewed in Spanish and English) and can check in online and passangers can check in 20kg for free.
My one point of contest with Avianca is that they advertise flights as direct that are not. I booked a direct return flight from Quito to Caracas a few months ago to arrive at the airport and find that I had to change planes in Bogota. Very irritating given that it vastly increased journey time and had me in a panic for a few minutes when I couldn't see any Quito to Caracas flight on the departures board. This is fairly common in south America but that doesn't make it any less frustrating.