Your motherboard and PSU are ready for the top cards out there. Video cards won't do much for you if you're using Photoshop standard version and Illustrator unless you use programs that deal with motions, such as Premiere, After Effect, and 3D. Since you're into gaming, I'd say get the most expensive one you can afford. You don't wanna get slaughtered by other players just because you're running a low-end card. A card that handles the latest games in high settings will handle any program you throw at it. I've never gone cheap on this piece of important hardware for my setup.
The 8800GT is a great card, but it only come with 512mb. Since you're willing to spend up to $350, you might as well the the faster 8800GTS that comes with 640mb. If you're willing to spend a little more, you can get the 8800GTX with 768mb...this card flies in any game out there. You'll never have enough speed when it comes to gaming. Get
this card from Newegg if you're not living in CA. Evga has the best warranty and their 90 upgrade program is a bonus. XFX and BFG Tech are also great.