Just for reference,

For a complete overview of what's out there and how relevant it is,
there's coinmarketcap.com and clicking "Volume (24h)".

Presently the coins with >1m/day trading are:

Bitcoin (30)
Litecoin (10)
Dogecoin (2)
Peercoin (1)
Auroracoin (1)

I.e. LTC's size = the next three's together x 2.5.