With PS3 Firmware v2.00+ you are now able to create Custom PS3 Themes. Below will be links to utilities used in their creation- updated as more are available:

Download: PS3 Custom Theme Tool v1.01 (English)

Download: PS3 Theme Previewer

Download: Program XMB 2.0 BETA v0.5.0.3 For PS3
Download: Program XMB 2.0 BETA v0.6.0.3 For PS3

Download: PS3 Theme Builder v1.0
Download: PS3 Theme Builder v1.2
Download: PS3 Theme Builder v1.3
Download: PS3 Theme Builder v1.4.1
Download: PS3 Theme Builder v1.5
Download: PS3 Theme Builder v1.6
Download: PS3 Theme Builder v1.6.1
Download: PS3 Theme Builder v2.0
Download: PS3 Theme Builder v2.1
Download: PS3 Theme Builder v2.3
Download: PS3 Theme Builder v2.3a
Download: PS3 Xross Media Simulator v1.0
Download: PS3 Theme Builder v2.4
Download: PS3 Theme Builder v2.5 (Update Only)
Download: PS3 Theme Builder v2.5 (Full)
Download: PS3 Theme Builder v3.0 (Update Only)

Download: PS3 Theme Creator v1.5 (with Sample)
Download: PS3 Theme Creator v1.6 (with Sample)
Download: PS3 Theme Creator v1.7 (FW 2.4 Patch)
Download: PS3 Theme Creator v2.0 (with Sample)

Download: PS3 Theme Extractor v0.7
Download: PS3 Theme Extractor v0.8
Download: PS3 Theme Extractor v0.9
Download: PS3 Theme Extractor v0.10
Download: PS3 Theme Extractor v0.11
Download: PS3 Theme Extractor v0.12

Download: PS3 Theme Generator GUI
Download: PS3 Theme Generator GUI r1
Download: PS3 Theme Generator GUI r2
Download: PS3 Theme Generator GUI r3