I dont usually bother squeeing about the visuals in software — function over form and all that — but here, in my not-so humble opinions, weve got two pieces of it that really benefit from an overhaul in the form of Tango. jEdit (4.3pre14 and up) because in previous versions its had a plain monochrome default set that are difficult to distinguish at a glance, and Opera because the new default themes in 3.6x (a black Vista type, and modified Classic one) are pretty hideous. So much so the Tango skin, put together from the icons by Tobias Wolf, is currently a very popular download.
Tango is a professional quality free icon set you can find out more about at http://tango.freedesktop.org/ if GUI design is something that floats your boat.
Heres an example of Tango icons in a 1by1 [a neat low-resource MP3 player] toolbar skin I knocked together. Click for the full image strip.
Colours have been reduced to a 256 colour palette, dithered to an XP grey background. (As far as I know 1by1 treats the background as transparent when rendering windows.)
jEdit and Opera are both steadily improving in other respects too (although theres still no option in jEdit to configure scrollwheel use and, whilst Opera has plenty of features, it lacks the flexibility Firefox has with extensions) but its nice in the case of jEdit to see people also committed to paying some attention to the gloss that affects how newcomers see the software prior to downloading and how we all interact with it. Opera, on the other hand, want lashing for issuing such an inappropriate default theme to XP users — whore still by far the majority userbase out there.