Hello there :]
I was always annoyed by this black line in the "Go To Symbol" toolbox : Damit, it should be gray like in the "Select Bundle Item" toolbox !
 In order to fix this, just put the "SymbolChooser.nib" file there : /Applications/TextMate.app/Contents/Resources/English.lproj/
Confirm the replacement, restart TextMate and enjoy.
Urbanose