Can't answer your question as posed - it depends on your usage.
SSD will improve boot and application start times. For most users, this is probably where you get the most perceived performance.
More Ram means more applications can be open at once. Some apps need a lot of memory to work well - Virtualization leaps to mind.
I can only comment on the SSD I use, which is the Intel XM25 Gen2 160GB. This is a great drive and I have no regrets with it, but I probably wouldn't choose it right now. The Gen3 Intel drives will be out soon and it seems like the "sandforce" drives have caught up to if not surpassed the Gen2 Intel drives.
If you want a fast boot, ssd, if you want to do heavy multi-tasking, then ram...get 8 gigs ram and a Seagate Momentus XT 500 gig hybrid drive...enjoy, and quit chasing it.