Here are some splash screens I created for OpenOffice.org, The GIMP and Exaile. Other apps will probably follow soon.
Please make backups of your current splash pixmaps before using new ones.
For OpenOffice.org: go to /usr/lib/openoffice/program and replace your "intro" and "about" BMP files. Names vary between distros.
For The GIMP: open /usr/share/gimp/2.0/images/ and replace gimp-splash.png.
For Exaile: browse /usr/share/exaile/images and replace splash.png.
All the above operations require root permission.
I'm also including the correspondent SVG sources in case you want to check or change something for yourself.
If you want to do other suggestions, please try to inform me about the place where the splash screens for those apps are located. I'm currently trying to find Abiword's splash image.
I hope you enjoy it.