valve spring compressor
I have a spring compressor that looks like a small puller. The two arms are not the same length so it is even when you grab the spring from two sides. The bridge that is attached to the screw portion stands about an 1" higher than the retainer. The only issue I have had is getting the arms attached low enough on the spring to compress it enough to get the locks out. I normally catch the long arm into the sring and then screw it down towards the bottom of the spring to ensure I have caught enough of the spring.
I have been able to remove double springs with a damper inbetween with this unit and as I recall I paid about $10 for it from one of the tool guys that show up at the local swap meets. I think the name brand was Cal Custom or Cal Hawk or something like that.