Apart from Perfect Money these are some of the options if you are looking for non-reversible payment methods when dealing with bitcoin.
1. Bank wire.
2. SEPA transfer.
Depending on the banks involved I think bank wire and/or SEPA transfers may actually be reversable. At least I've heard anecdotes of people's bank account going negative after they've withdrawn the agreed upon payment, due to the bank transfer being reversed.
There is a crypto-currency called tether. Tether is always worth exactly $1 and uses the blockchain technology similar to other crypto-currencies. Its becoming more and more popular in the last few months.
https://tether.to/Be careful when using tether. These are basically USD IOUs that are not necessarily 100% backed by its face value. Use them for transactions but try to avoid holding significant amounts of tether at any given time, lest we see the joys of fractional reserves in crypto.