Recently, I met a Colombian, we met each other through chat at first, and we continued speaking for a while, and eventually I showed him a video of me speaking Spanish, and we has impressed by my abilities and near mastery of the accent. He was also wondering what I thought of his English accent. So we exchanged some clips and I was surprised by the very good accent he had in English, but later he started speaking again in Spanish and I was astounded by the very neutral sound of his accent. It seems that where this speaker lives the Spanish spoken there had a very neutral sound, which makes it easy for speakers to develop an almost natural sounding English accent. This particular speaker was from Santa Marta and as far as I can tell the accent there is quite neutral, which would be a definite plus for leaners of Spanish who would prefer a neutral and less thick way to develop listening skills, while later making your way through the more thick accents.
I researched a little more and found a great database of speakers and their accents in English. The database is called the Speech Accent Archive. The website also has recordings of natives, which is really handy for illustrating some of the differences between dialects in the United States.
