Here are a few of my favorite blue shades. In no particular order (other than darkest to lightest/brightest) I present:
Mariner by butterLONDON. I love this rich navy blue. Acquired during a giveaway for Earth Day this year, this is one of the best navy's out there.
Yoga-ta Get This Blue by OPI. AHHHH! This was a recomendation color from my friend and fellow nail polish slut, Heather. I love the shimmer in this medium blue polish. I'll re-swatch it eventually. This is a crappy pic from my iPhone.
Aqua Baby by China Glaze. Summer blue - need I say more. Not only is this aqua amazing on the hands but it's quite the flashy color for the summer months.