If you want to use a higher resolution on your linux console, you have to add the specific option while loading the kernel.
i.e: kernel /vmlinuz-2.6.25 root=/dev/sda3 resume=/dev/sda2 vga=0x0325

Problem: The settings differ depending on your graphics card.
But: There is an easy way: hwinfo

[ sudo ] hwinfo −−framebuffer

Example output:
Mode 0x0307: 1280×1024 (+1280), 8 bits
Mode 0x031a: 1280×1024 (+2560), 16 bits
Mode 0x031b: 1280×1024 (+5120), 24 bits
Mode 0x0305: 1024×768 (+1024), 8 bits
Mode 0x0317: 1024×768 (+2048), 16 bits
Mode 0x0318: 1024×768 (+4096), 24 bits
Mode 0x0312: 640×480 (+2560), 24 bits
Mode 0x0314: 800×600 (+1600), 16 bits
Mode 0x0315: 800×600 (+3200), 24 bits
Mode 0x0301: 640×480 (+640), 8 bits
Mode 0x0303: 800×600 (+832), 8 bits
Mode 0x0311: 640×480 (+1280), 16 bits

Thanks to Gerd [de] for the hint.