If you use bitcoin-qt you can use the command line.

https://en.bitcoin.it/wiki/Running_Bitcoin#Command-line_arguments

Most clients have a version. With the interface you can find the console under ->Help. You can also launch a server:
bitcoind -server
and then use bitcoin-cli

The commands you want are:

bitcoin-cli getrawtransaction  HASH
(gets hexadecimal byte sequence in hexadecimal)
bitcoin-cli getrawtransaction  HASH 1
(gets the JSON-parsed version)

bitcoin-cli getrawmempool
(gives the mempool at your local node)

If you access the console from bitcoin-qt, drop bitcoin-cli.

You can also find an online mempool explorer in:

http://webbtc.com/mempool