Upgrade Questions

First off, I post here because I think that the graphics card would be the best place to start. I understand I don't know everything, or even that much for that matter. So I would like some advice please.

I am an avid MMO'er and have had my current setup for about 3 years and am getting to the point that I think some changes are in order. I don't want to get too crazy with upgrades, basically I am looking for better performance but would love to stay around the best performance/price ratio. I would hate to buy a card today to see it drop significantly in price next month. Yes, I understand technology changes on a daily basis and what I buy today wont be worth that price tomorrow, but we all know that most things hit a plateau for a bit at some time in their life cycle. My goal is to find things that are just starting in that plateau.

Current components:

Motherboard - ASUS M2R32-MVP AM2+/AM2 AMD 580X CrossFire ATX AMD Motherboard
PSU - Rosewill Xtreme Series RX850-D-B 850W
CPU - AMD Athlon 64 X2 6000+ Windsor 3.0GHz 2 x 1MB L2 Cache Socket AM2 125W Dual-Core Processor
GPU - 1x SAPPHIRE 100242L Radeon HD 4850 512MB 256-bit GDDR3 PCI Express 2.0x16 HDCP Ready CrossFireX Supported Card
RAM - 5 GB CORSAIR XMS2 (2 x 2GB, 1 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400)
HDD - Western Digital Caviar Blue WD5000AAKS 500GB 7200 RPM 16MB Cache SATA 3.0Gb/s 3.5" Internal Hard Drive
OS - Triple-boot XP, Vista and W7

Maybe get another 4850 and crossfire them? Maybe change something else? Any comments or advice are welcome.

Thank you!