i have a evga x58 sli3 mobo. Can I only use nvidia gpu with sli mobo?
You can use AMD or nVidia cards without a problem your board also supports crossfire so it gives you a pretty unrestricted selection to pick from.
If you're planning on a 3-card SLI or CrossFireX configuration make sure you select graphics cards that support 3-way SLI or CrossFireX. Some of the graphics cards will only support 2-way SLI or CrossFireX.