What is the third most popular cryptocurrency?

[Strongman]

Besides Solidcoin.

[Bitcoin Oz]

Probably Bitcoin>litecoin>namecoin

[Strongman]

Probably Bitcoin>litecoin>namecoin

Namecoin isn't technically a currency. It's a naming system. Anything below that?

[matthewh3]

Probably Bitcoin>litecoin>namecoin

+1

NMC can be bought, sold, traded and transferred.  Sounds like a store of value and a means of exchange to me.  Even if it can do more than that as well.

[Stephen Gornick]

Besides Solidcoin.

Are you limiting this to proof-of-work currencies?

MintChip would probably be #2, even though it hasn't launched yet.

Second Life Lindens is virtual currency, but hardly really has no crypto component.

Pecunix might rank, but it is just a ledger system for a gold backed asset.  And if Pecunix gets in, then so does Liberty Reserve and all the other centralized digital curencies.

I don't know where Ven might fall, I can't picture it as being anything more than an electronic ledger either.

Open Transactions isn't a currency but it probably gets honorable mention as a container / transmission network for them.

So ... looks like in terms of dollars of all coins at the current exchange rate you would have

Bitcoin: $130 million USD (Coins in circulation X current exchange rate)
Litecoin: $0.25 million USD (Coins in circulation X current exchange rate)
Namecoin: $0.10 million USD (Coins in circulation X current exchange rate)

That may not define "popularity", though as Namecoin has more transactions than Litecoin, for example.  But it you consider transactions, Bitcoin Testnet has more than both Litecoin and Namecoin.

Here's a block explorer for them:

 - http://ufasoft.com/coin/blockexplorer

Namecoin isn't technically a currency. It's a naming system.

Dot-bit.org is a naming system.  The currency it uses is Namecoin.    Namecoin can be used for other purposes than just registering domain names under the .bit TLD.