Rather than the first five, I'll highlight some of my notable first trips ...that don't yet overlap with the other posters first trips!
I'll try to get some more pictures up as the day goes on.
One of the first places I traveled to in Chile was Quintay. Its a little old whaling town along a rocky coast. For only around 500 pesos ($1) we entered into the museum and wandered around the ruins of the old buildings. It also had one of the most gorgeous sunsets I've seen in Chile.
I've been to Maitencillo a zillion times, give or take a few, but still remember very clearly my first and second times there. My first was the weekend of the 18th of September, and I very angrily climbed into a car at about 4am, worried the driver had been drinking, and ended up on the beach of Maitencillo along with a few thousand other university aged partiers.
An hour's bus ride away from the ocean, and another 20 minute truck ride with a girl who must've been the original inspiration for the jokes about female drivers, brought me to Quillota. Its a gorgeous area inland that seemed perfect for planting all sorts of things- our host had everything from avocado to a cactus garden. Despite my trip being mostly ruined by the owner of the house promising to kill me in my sleep because I'm from the US (I slept nervously in a tent in the neighbor's front yard instead), I did come away alive and with some nice pictures of the scenery.
About an hour's bus ride from Valparaiso, Horcon is little fishing village famous for its empanadas and nudist beach. Through the workings of a guy friend I made here, he sent me off with his girlfriend and all her friends to a cabin for the weekend. As much as I really wanted to get to know some Chilean girls, I was fully thankful the second night when carloads of guys showed up the second night for a barbeque, and to break the mood. Despite many future trips, as a good friend now lives there, I have never actually been to the nudist beach.
I love this city. I've been to Los Andes a number of times, and absolutely love this peaceful, hot (in the summer), cute little city surrounded by mountains and campo. This was actually one of my first trips in Chile, as I took off by myself to go camping with a friend of a friend who'd I'd only talked to on the internet. It sounds quite sketchy, I know, but he picked me up as I jumped off the bus in front of a gas station outside Los Andes and we camped up in the mountains with his friends, and I got to meet some real huasos (though I couldn't hardly understand a word they said as the people who live in the mountains seem to have a rather mumbled, ungrammatical way of speaking). Again, I lived to tell the tale!
Some of the other cities I've traveled to in Chile include:
South: chiloe (4x) (ancud, castro, some other little cities on nearby islands), puerto varas, puerto montt, frutillar, villarica, pucon, temuco, valdivia
Middle: rancagua, santiago, limache, quillota, los andes, lo campo, san felipe, llay llay,
Middle coast: quintay, valparaiso, vina, concon, ventanas, pechuncavi, maitencillo, horcon, quintero, maitencillo, zapallar, cachagua, san antonio, isla negra
North: la serena, valle del elqui, san pedro, calama
My top desired trips include: Juan Fernandez, Iquique, Rappa Nui, and various wine country trips in the center inland.