There is no standard tx fee.  Non spam tx can be sent with 0 BTC and will be considered valid.  Miners have the choice of what tx they will include and can exclude tx that have too little (or no) fee, but almost all include all valid (non spam) txs regardless of fee.

About spam.  To protect the network the protocol requires a fee of 0.0005 BTC if the inputs are less than 1 bitcoin day old*.  For example if you received 1 bitcoin and wanted to spent it you would have to wait 1 day to avoid a fee.  If you received 10 bitcoins you would need to wait 1/10th of day.  If you received 0.1 BTC and wanted to spend it you would need to wait 10 days.

If you wait that long (or longer) you can send coins without any fee.  If you want to send it early you need to pay the spam-fee.  Other nodes will declare your tx invalid and refuse to relay it if you don't pay the fee.  The client also needs to be modified to get around the fee.  Since unmodified clients will refuse to relay the tx you run the risk of having the tx in limbo or not seen by recipient if you modify a client to break the spam rules.

The important thing is the spam fee isn't designed to "make money".  You can simply wait (or keep some "old coins" handy) and never pay it.  The spam fee is designed to protect the network from a DOS attack involving massive amounts of tiny transactions.

*technically the limit is in blocks but it is roughly 1 bitcoin day which is slightly easier to remember than  57,600,000 satoshi blocks per byte.