Multicore Prozone Alternative
The trick to clean soldering is to figure out the proper solvent for the flux you're using-- or even if you should clean it up at all.  For example, in my lab I only use water soluble flux.  It cleans up well with, you guessed it, water!  I just rinse the PCB's off in the sink with hot water and my boards are nice and clean.  Just make sure that's it's good and dry before powering it up.  But it turns out that isopropyl alcohol doesn't work well at all on it, and leaves a weird residue.

Other fluxes will clean up with isopropyl, but some require things like acetone (yuck!).  But keep in mind that some fluxes will never clean up well, and that's just the way it is.  For example, the "no clean fluxes" will often leave a residue that is unsightly but harmless.  Standard rosin core flux is the worst for residue, in my opinion.

An alternative to 99% isopropyl is the 97% stuff that you can get at most corner drug stores or pharmacies.  It costs a lot less than the 99% stuff, and does almost as good of a job.