Elkhorn fly lines are quality and affordable.  I tend to not take as good a care of my line as I should, so the Elkhorn line makes perfect sense.  Also, I don't know anywhere else you can find a pink (dusty rose) fly line for the ladies.

Fish Creek and Stone Creek lines are excellent lines.  They are supple and slippery to shoot line a long way.  They have a quality coating that stands up to dirt, grime and weather.

The TL Johnson lines... what can I say, other than their Synergy line of rods are their premium performance products and their fly line is no exception.

How do I know what Fly Line weight matches my Fly Rod:
If you buy your Fly Rod new, you should already know what weight line it needs to properly load the rod, but if you inherit the fly rod or purchase it at a garage sale, the fly rod should be marked with a specific weight right above the fly rod grip.  Some fly rod manufacturers use different markings... for example, your fly rod may have 804-5; that could mean the rod is 8'0" length and either a 5 piece 4 weight line OR and 8'0" length 4 piece 5 weight (easy way to decipher, count the number of pieces).  Some Fly Rods spell it our in plain english... ie; 9'0" 6 wt, or 7'6" 3wt.