I've created my own separator cards (loosely based on http://www.boardgamegeek.com/filepage/36272/carthaginians-do...
It includes separators for all Dominion games up to Dark Ages (and probably more, when they come out).
There are 2 versions to choose from: landscape or upright. So you have the appropriate card separators, no matter how your box / case layout is.
I've redone all the work in Adobe Indesign CS4 & Adobe Photoshop CS4 and if you write me (commenting the before-mentioned blog-entry or by email) I'll send you all the data you need to do your own set of separator cards for any language or expansion you want. You only have to exchange the text, which is really easy if you ever worked with Indesign. Only downside ist that.. well, you need Indesign CS4 or newer ;-)
If you use my work to create your own version, the only thing I demand is to be notified (here or on my blog). And of course follow the above mentioned license (in short: do whatever you want as long as it's non-profit and you mention me, preferrably by linking to my blog's page).
For more information pictures, how to use the separator cards, ... visit my blog: http://www.phenx.de/dominion-kartentrenner/