Future Upgrades

I am currently in the process of upgrading my system to finish the final parts of my build. I have several things that I need to purchase and need some recommendations on the last bit. My current budget is $290, but as I will be upgrading in quantities, the price is not firm.

Budget: $290

My current build is as follows:
CPU: Intel Core i5 2500k (not overclocked, stock heatsink)
Mobo: ASRock Z68 Extreme 3 Gen 3
GPU: GIGBYTE Radeon HD 6670 (laugh all you want)
PSU: 350W Crap
HDD: Seagate Barracuda 160GB 7200RPM
Case: Rosewill Challenger

The Upgrades I Need:
-PSU
I'm looking for a PSU with some overhead. It needs to be able to power a boot SSD, a 1 TB HDD, a DVD burner, three case fans (one LED), the non stock heatsink, and in the future be able to run two GPU's running Crossfire or SLI
-Heatsink
Not picky about this part as long as it does something better than the stock heatsink. I'm looking to try and run at 4.0 GHz, and that seems quite possible with the Hyper 212.
-DVD Burner
Again, not picky. Something cheap, that will last and has a good overall rating. I have some options, but I want to assure that I'm making the right decision. Solid black is preferred.
-Boot SSD
I'm siding with the Crucial M4 128GB, as I'm worried that with WoW, OS and the several other games, that I'll be filling the thing up to fast.
-Storage HDD
Something big that won't crap out on me. I'd say a good bet would be 500GB.
-GPU's
This build will as some point run SLI/Crossfire and was hoping to find a GPU that can support this with the case space provided. I was siding towards the 560 TI as I don't need a huge amount of power, just enough to get me by on current and close next gen games.


TL;DR
Here's $290. When upgrading, should I start with the PSU, Heatsink, DVD burner, SSD, HDD or GPU first? Of those, for $290, what would you purchase and why?
I'm leaning more towards dropping $100 on the PSU as that seems the major limiting factor, then the heatsink and then the SSD. The GPU is holding out for the gaming I'm doing, with Skyrim running on high at I'd say 30 FPS or so, and it seems like the last thing I really need at the moment.



Edit: Also, at one point, I'd like to "rice" my system and add a bit of flash. I was hoping to get the LED temperature reader that sits in the dvd drive slot as well as some string LED's at some point in the future, if any of you have reccomendations for those.