NEVER NEVER EVER by the one dollar nail polish! It is CRAP and even though it is only one dollar, it's a total waste of money! Some good nail polish brands are OPI, REVLON, and CHINA GLAZE. Essie and Color are iffy, they both require several coats and if you do to many it gets thick and peals off. Other than those I haven't really used any other good ones.
Some tips to look out for are:
Don't buy any that are store brand and/or cheap.
The best are $4-$8.
Watch out for the reds because sometimes they are to dark and make your finger nails look like they have blood on them(learned that the hard way).
Match your outfits to your nails (if you forget they may end up clashing).