Seednodes are a misnomer as that are not necessarily nodes which have Bitcoin running.  Instead it refers to standard DNS servers with A records that new Bitcoin nodes use for bootstrapping to learn of peers.

Currently, Bitcoin master shows these four:

 - bitseed.xf2.org
 - dnsseed.bluematt.me
 - seed.bitcoin.sipa.be
 - dnsseed.bitcoin.dashjr.org

Source code:

 - http://github.com/bitcoin/bitcoin/blob/master/src/net.cpp#L1123

<code>
// DNS seeds
// Each pair gives a source name and a seed name.

// The first name is used as information source for addrman.
// The second name should resolve to a list of seed addresses.

static const char *strDNSSeed[][2] = {
    {"xf2.org", "bitseed.xf2.org"},
    {"bluematt.me", "dnsseed.bluematt.me"},
    {"bitcoin.sipa.be", "seed.bitcoin.sipa.be"},
    {"dashjr.org", "dnsseed.bitcoin.dashjr.org"},
};
</code>