Upgrade a MBP(8,1) dual i7 to 16GB RAM from 4GB or to a SSD?
16GB Memory + 128GB SSD + Data Doubler from OWC (or analog from ebay) to put SSD into it. Only caveat would be if your MBP is one of early ones that had Optical SATA connector capped at 3Gbps. Then if you want SSD to be as fast as possible it's better to put it in place of HDD.