More RAM is always a good thing. If you are running your RAM as dual-channel, you should be in good shape. Pop in another gig and away ya go.
"Mem Doubler"? Looks cheesy to me... all it is doing is adjusting your page file. Scrap it and get more RAM. RAM is always faster than your hard drive.
For my memory usage, I use Yahoo Widget Engine's Memory Gauge, set to always be on top. That way I always know exactly how much RAM is in use.