How can you find out what is the latest block number? When running a fresh client, or after not being connected for a while, the client takes some time downloading new blocks. How can you find out what is the target block number (the id of the newest publicly available block)?
All these sites display the total block count:


http://blockexplorer.com/
http://bitcoincharts.com/
http://bitcoinwatch.com/


BlockExplorer also has an API that among other things lets you get the latest block count.