There are innumerable stethoscope threads, all saying largely the same thing. I'll break it down by certification level:
Student/below EMT-B: Take what you're given, and wait a bit before buying anything.
EMT-B or equivalent: How clearly do you need to hear those Korotkoff sounds? Get something reasonably-priced. I use an ADC ADSCOPE 630 which cost me about $30. It's heavier and slightly less comfortable (stiffer earpieces) than the Littmann scopes I've had a chance to use, but it's more than adequate for my needs. Littmann lightweights are also in the <$100 range. The consensus is to stay away from dual-tube (Sprague-Rappaport-style) scopes, which aren't to be confused with dual-lumen scopes.
ALS providers: Why would you be listening to my lowly opinion?
For identification, get a color that doesn't look completely ridiculous, but isn't black or navy blue. Put your name on it securely; Littmanns have tags, one poster suggested attaching an ED patient bracelet with your name on it, and there are always Sharpies (my method) and tape.