Best bang for my buck when it comes to storage & speed
 

I want to upgrade to a couple new hard drives, want to run them in RAID0, or get 1 single fast drive and 1 large storage drive.

Which would be the best bang for my buck, looking to spend around 120-140 on drives.

fastest mechanical drives on 7200 RPM that would fit your bill are the Samsung HDDs. You can get 3x320GB model and raid them in 0 mode or get only one and a large 2 TB model, also from Samsung, all this on newegg. I have both models and I am very satisfied. In fact I am considering getting another 2TB one. The 320GB is the fastest drive on 7200rpm on the market, reading speed is around 160MB/s, tested on my rig with hd tune 2.55.

I'd be ordering from NCIX because they accept interac, and from what i see they don't have sammy drives anymore :(

How about 64gb C300 + Barracuda XT 2TB? Tough to beat that combo. Or 128gb C300 and 1TB Black if you dont need 2TB.

Wait 120-140 total or each? If that is total then you cant go SSD and probably a pair of 640gb blacks (or similar) would be the best bet. Assuming you have a sata 6g board

2TB Western Digital Caviar Black will wipe the floor with the Samsungs, especially if you short stroke them. 1TB Blacks Short stroked in RAID 0 are also still one hell of a power house.

$140 in total, well realisticly i have about 160 but i have to factor in HST and shipping :\
I'm eyeing an SSD, but i have an old mobo (M2N-E) so i wouldn't have TRIM, I also need storage moreso over speed as im running on a 200GB HDD right now and it's starting to get brutal having to delete almost everything every week.

Are the Black's confirmed to be using 500GB platters? If not, even Seagate's 500GB platter 7200.12 drives are faster, and also very inexpensive.

However, I would go for a small capacity SSD (C300 already suggested would be my choice as well) and a larger storage drive. You could even get just the SSD and use whatever you have now for the storage drive. That would still be way better than any mechanical RAID 0 setup.

EDIT: C300's have good garbage collection, minimizing the need for TRIM.

To answer your question about 2-platters:
Roundup: New Hard Disk Drives with 1 TB and 2 TB Storage Capacities. Page 3 - X-bit labs
Note this is the "FAEX" version of the Caviar Black, with slightly lower power consumption. The older FALS version had three platters.

OP, you should be able to have TRIM if you DO NOT USE THE MANUFACTUER'S STORAGE DRIVERS. Of course this will be impossible if you want an SSD + RAID on your motherboard, because enabling RAID means you need the drivers anyway. Doesn't the "N" in M2N stand for nVidia? If so I'd go for SSD + hard drive, or just one fast hard drive because nVidia's outdated storage drivers gave me inconsistent performance and a headache whenever I changed the graphics drivers but didn't want to touch the other drivers.

Yes it's running the 570 SLI nvidia chipset.