Ok, Sold states are very unstable as of now, there are many problems with them, I would wait until they are a little older and more mature. The only "mature" SSD are from Intel and they are far to expensive $/gb.
Solid state disks are so fast because they have no moving parts and are therefor not limited by the speed at which the "platter" can spin, the faster the platter can spin the faster the Head can read information from it, the cache is a preload so information is not being written from when you clock there's some sort of buffer of information. Hope you understand this.
Now to pick a HHD for you they are for more economical
What will you be using your HDD for?
With video editing you won't want SSD because their capacity is too small, unless of course you are editing tiny videos . What the ladies and gentle here said is true, the SSD isn't worth it for the desktop yet.
If you're doing serious video editing then you'll be moving around a lot of data and in that situation if you're serious about it, grab some sata2 disks and stack them in a RAID 0 array.
For gaming you'd also benefit from a RAID 0 because it'll be able to load textures and other data faster.
For games/apps that load lots off the hdd its good to have two separate hdds so you can put your OS + swap file on one physical disk and let your game load off another physical disk. That way its not all fighting for the same read/write heads.
I recently read an article benchmarking Crysis with various performance hdds and there was an improvement in fps on faster drives because Crysis reads the hdd a fair bit. That held true for Crysis but if you're playing a game like Warcraft 3 then the boost in hdd speed wont' matter because the game isn't heavily trying to read from your disk all the time.
Also if you want speed without an array then consider 10k or 15k rpm drives.
I've been considering faster drives myself and I like the SSD's access time but not the throughput.
x_2fast4u_x was right about the mature SSDs being far too expensive. For the cost of an x25e you can raid 0 a pile of normal drives.
For my home system I'm thinking of getting 3 x 32GB SSD for a raid 0 array. Since raid 0 comes with the paranioa of 1 disk going down and take everything with it, I'm going to have it backup important stuff to a normal drive. I'm not certain about it yet though because I want to have two of those setups and its a bit pricey.
As for the raid 0 data security: I looked at doing a raid 5 instead and sacrificing a drive for data security but raid 5 kills the overall write performance because it has to update parity data all the time. It still reads/writes fast, but doesn't get the full benefit of the write performance. The next option was raid 0+1 which skips the parity writing but costs double the amount of disks which is too expensive for my taste so its looks like an extra backup drive would be my best solution.
This site has hdd charts you can view to see some differences in performance:
I googled up RAM SSDs because I remember they were blazing fast and it seems there has been a bit of an improvement with them. Fusion-IO has the IODrive with 800MB/sr and 600MB/sw and it is supposed to be priced at $3k. Crazy.