Seeking upgrade advice

Hey all, I was looking for some advice since I'm pretty much in dire need. I built this computer about 3 years ago on a budget and I'm looking to upgrade now. I'd like to know in what order I should be upgrading and a recommendation. I'd still like to be building a semi-budget computer, but I plan on doing the upgrades over the course of a few months so I'm not too pressed.

As a note, I plan on buying a new hard drive soon (1 TB) and I just bought the case.

HDD: Western Digital WD Blue 160GB (http://www.newegg.com/Product/Produc...82E16822136075) + 250GB HD from my old computer
RAM: GeIL Value PLUS 4GB (2x2GB) 240-Pin DDR3 (http://www.newegg.com/Product/Produc...82E16820144461)
CPU: AMD Phenom II X4 955 Quad-Core Processor (http://www.newegg.com/Product/Produc...82E16819103808)
Graphics card: VisionTek 900329 Radeon HD 4850 (http://www.newegg.com/Product/Produc...82E16814129163)
Motherboard: ASRock M3A770DE AM3 AMD 770 (http://www.newegg.com/Product/Produc...82E16813157176)
Case: COOLER MASTER HAF 912 (http://www.newegg.com/Product/Produc...82E16811119233)
CPU Fan: COOLER MASTER Hyper 212 (http://www.newegg.com/Product/Produc...82E16835103065)
PSU: Antec 500W (http://www.newegg.com/Product/Produc...82E16817371004)

I play a lot of random stuff, like right now I'm playing Forge and Rift. I'd like to play Rift on medium-high settings. I'd also like to pick up GW2 and play that on relatively high settings too. In general, I'd like to play games on medium-high. I'm not a full PC gamer so I don't need everything to be maxed out.

Thanks in advance for any help. I've been posting in here kinda frequently lately and I appreciate all the responses and helpfulness. I'll try and answer any/all questions as quickly as possible.