And if you want a free solution, there is bcompiler, eaccelerator/mmcache and some others. Be aware that the feature set and usability of different solutions varies widely though, and the deployability and robustness of scripts in terms of whether they are immune to corruption from CR/LF conversion during installation also depends on the choice of solution. Be sure to try the evaluations from different providers and ask questions about the products so that you pick a solution that best fits your needs.
There are also several other products in the $40-99 range, but, bluntly, they are mainly crap (insecure, buggy etc...). Personally, I would stick with either ionCube or Zend. As for SourceGuardian, it's most certainly the 3rd choice