I just picked up a Dell server with dual 771 Xeons, and I put dual quad cores in there, it's crazy, the FB-DIMM memory is a bit expensive, I was able to buy 8x 1GB modules for $4 each, but if I could bring a server to the DC, I wouldn't hesitate to max the board out (8x 4GB = ~$300-400). A DDR3-based system would be pretty cool too. In that case, since I like to go absolutely nutters overkill with systems, I would put 64GB+ in there and even that would only cost a few hundies. I constantly look at boards that can take 768GB and I'm like, why not me? But, >2GB is all we need, and it's a good thing I picked up that extra gig from BitVPS. As a temporary fix, I'll probably get BitVPS to sell me even more memory, another gig is going to be pricey but if that's the bottleneck, let's dooo eeeet. But yeah, if they let me bring a server to the DC, I'd put SSDs and basically just take the specs way over the top. I want the site to be able to scale.
If you go the dedicated hardware route, upgrading to an SSD for the database is going to probably offer the most bang for your buck, much more than jumping past 8 GB of RAM. Random seek time might not be everything when it comes to database performance, but it is a lot of things.
There are few better ways to solve software problems with hardware than running website databases off of SSDs.
