josejones: I'll throw in my 10 cents for you, having come from a 3d animation/ video editing/ dvd-authoring background.
Doesn't look much like SATA4 is anywhere on the visible horizon, which dissapoints me too, as it's clear SSDs could go even further, tomorrow!, given the right connectivity. However, unless you have a particularly large budget, you aren't going to be able to set your system up soley with SSDs anyway, given you're going to be outputting large numbers of high resolution image files for your projects.
RAID is more hassle than it's worth, in my opinion, considering that Windows 7 supports SSD TRIM (removes deleted files from your SSD as you delete them, rather than the SSD having to erase before write when accessing previously written-to sectors) only in non-RAID configuration. Plus the performance from an SSD flattens that of a HDD, even without RAID. I've only ever had SATA2 SSDs (with maximum read speeds of 270MB/s), and these still blow me away. Current Intel 520 series SSD's offer transfers of 550MB/s across the SATA3 interface. With SSDs, don't go skimpy on size. Obviously you'll have a tight budget, but you'll want to get a 520 series with a minimum of 120GB size - that way you'll be able to install Windows 7 x64 (25-30GB depending on version) all of your other software apps, and still have space for placement of your project source files. Not to mention furure-proofing as best you can. The 520 series 180GB is what I would buy, if I was upgrading right now.
You can experience large performance gains in video editing/graphics applications, just by spreading tasks across multiple disk drives. It's not healthy for SSDs to 1. defragment them (as every erase/write cycle takes another chip of the lifespan of the cell, and defragmentations are erase/write heavy - plus there's no performance gain, as an SSD can read from any cell with the same super-low latency) and 2. use them for the Windows "Page File" or Photoshop "Scratch Disk" as these are both forms of virtual memory and again, involve plenty of erase/write to a small portion of the disk.
Ideally, you'd have 3 disks in your setup:
1. Your 120GB (or greater) Intel 520 series SSD - accomodating Windows, program files, project source files, and uncompressed video files you want to review with smoothest possible playback (in essence, everything which your computer will be reading from, if possible)
2. Your existing 500GB HDD (Create an initial 10GB partition, and set this as the volume for your Windows Page File. Then with the remaining space create a second partition, which you can use for storage of project files not currently in use, or projects too large to fit on your SSD, etc.
3. A new 2TB HDD (2TB offers the best price vs. size ratio at present). Buy Western Digital rather than Seagate, Samsung etc. WD delivers far superior accoustics and temperature regulation - I've been frustrated by every Seagate or other brand disk I've ever owned by the pulsating harmonic hums or over-pronounced read chirps they produce. (Create an initial 20GB partition, on which you'll place Photoshop's "Scratch Disk". Then create a second partition with the remaining space which you'll use to output/write to from all apps, and hold your rendered images.) WD Green drives offer best possible accoustics, but Black drives provide maximum HDD performance - I'll let you decide.
With this setup, when you're using Photoshop, Windows will be accessing the 500GB for it's virtual memory. Whilst Photoshop itself will be accessing the 2TB, ie: neither will be hindering the other's performance. Doesn't really matter which drive you keep your image files on, as the actually image information is only accessed during file open / file save, etc.
I've seen performance gains of 30 - 50% when reading source files from disk A, and outputting completed frames to disk B, as opposed to reading source and outputting to one disk A. As you know HDD's operate with a needle, which can only be in one place at a time, so it's ideal to have one disk doing just one thing reading or writing.
I can't tell you how to set up your files, but as an example, for best throughput, if I was using Maya, I'd want my source files, textures, scenes on disk A, and my output directory on disk B. Or with compositing software such as After Effects, again I'd want my source image sequences on disk A and my output ones on disk B. If you can have the source files on the SSD, that's a bonus as the Windows Page File can operate individually on the 500GB disk, you're reading from the SSD, and completed frames are outputting to the 2TB disk - none of the operations are stacked onto a single disk, so the pipeline is free-flowing and quick.
Coming back to reality, if I was to build your system right now, I'd get:
Intel i5 2500 (it's the best unit for price/performance ratio at present)
Transcend 4GB DDR3 x 2 (or x 4 if you feel you need 16GB of RAM) (I find Transcend very cost efficient and highly reliable)
ASUS P8Z68-M (7 SATA ports, 2 x PCIe x16, max 32GB RAM, etc. Or whatever good, low cost, feature rich motherboard you can get your hands on in your country)
Intel 520 series 180GB SATA3 550MB/s SSD
Western Digital 2TB Caviar Black (You'll want this now that you've taken over doing the videos and DVD work.)
Obiously once Ivy Bridge is out, that changes the recipe slightly. But I believe Intel 520 series and WD Black 2TB will still be your best storage solutions at that time.
Very important thing to consider is bargain hunting. Local is often worst in terms of price. I notice almost every company is a reseller. Try and hunt down the wholesaler in your area. One place will generally charge 5% more or less than the next, which gives away where they sit in the chain. In my country Alphacity.co.nz which I've used frequently is offering the best prices. Better still than another local wholesaler. They trade overseas as TigerDirect I believe.
If you don't get what I'm going on about with the different tasks allocated to different disks, please let me know and I'll try to explain it better.