I'm in a similar situation right now! about £500 disposable income at the moment and this is my plan of action:
1. Getting a whole new wardrobe, i haven't new clothes in a couple of years. I just bought a new expensive watch and new boots and i will need jeans, tops and shirts
2. Upgrade by DVD collection to Blu-ray. I'm well into this now at roughly 60%
3. Get those insanely expensive and rare model kits I've always wanted
4. Also buying better quality food from M&S and Waitrose. It's hard to believe but you really start to feel the difference in yourself after a couple of weeks (but that also be because i cut out all the junk food)
5. Spending more money of health products to look after myself from Boots and Holland&Barrents. Starting to take multi-vitamins/wellman stuff and better quality aftershave, toothpaste, mouthwash etc.
6. Pamper yourself for better health, go to the Dentist, Podiatrist, Massage and Waxing more often
I'm already in a good expensive gym and my computer is already a beast so i won't need to upgrade for a while but if it did then that would be pretty high on my list too