Need a Good place for large prints online

Hey Guys,
I'm looking at doing a few LARGE prints (smallest being 30x20) in all black and white. Since It's probably not the last time i'll be doing this, I'm hoping someone can shed some light on where I can order from and have good results. I'm guessing one of the shots will be in the 60x40 range and all will be black and white. If anyone can point me in any direction they actually trust i'd really appreciate it. I've heard b&w requires an actual b&w printer for better quality, but again, just what i've heard.

Thanks again! mods if this is in the wrong area i do apologize.