Without any serverside binaries all php encryptors can be easily decrypted - with serverside binaries I personally use Ioncube Encoder and am very enthausiastic about it.
I often use IonCube. I like the online encoder that I can encode single files for 10 cents each. So, you can protect one or two files with the most important portion of code in it and give out the rest of the files unprotected. I usually like to do that when I have a single domain license type of script. I protect the index and functions. The index holds the domain check and the functions holds most of the routines that are required for the script. That way the template system is untouched and it can be templated easier by the end user.
If you want no server side requirements, as eiso said, 'encrypters' are crap. If you want no server side requirements, I believe that obfuscators are the better option...
I use Ioncube too. If you wanna protect scripts you should alos use a licensing system like PHP Audit. Oh and you say your looking for Obfuscators, try looking in Tiwstmyarm's signature, lol