Spec me a small updrade (warning: old computer inside)

[Sudden]

I feel like upgrading my computer. No particular reason as such - just want to improve performance a bit if I can. Spending limit - around £100 but flexible. It is an old spec (I bought it around 6 years ago with an aim not to get a new one until I really had to. I can still run games like ME3 on full without issue so don't see a need to do a massive upgrade. Only new components have been a lil bit of extra ram and stuff upgraded due to returns under warranty)

Current spec:

EVGA 780i FTW edition motherboard
EVGA GTS 250 (1gb) graphics card
4 GB OCZ Platinum Ram - DDR2
x6800 core 2 due extreme (2.93 ghz - oc'd to 3.2 ghz)
150 GB Raptor HD + other HD's for storage
Tagan 900W (I think) PSU

Anyone have any ideas if there is anything I could add/replace to give a performance boost? As earlier - don't want to spend on a new rig instead.

 

[Sudden]

Have windows 7 x64.

Looks like SSD is the way to go. Any recommendations on a good one?

Sasahara above mentioned maybe a graphics card instead. I will continue playing games on this rig, depending on what's out there. Hitman is the current game which i'm thinking about, though might just get it for the PS3 instead. Is there any GPU out there which will be give me a worthwhile boost given the other hardware limitations?

 

[Sudden]

Does the faster write still help given that I am limited by Sata 2? Also - do I need any cables etc. in addition to standard HD ones to install a SSD?