It's a relatively common practice for alliances--especially larger alliances with widely disparate ranges of wealth--to encourage new members to post "help me out" trade offers. These 'offers' aren't actually meant to be taken up by anyone outside the alliance; rather, they're a way of asking for help getting started. Unfortunately, these offers also tend to clutter up the trade offers list.
I'd like to see something implemented that filters out these offers, so that only alliance members see them. I suggest that new trade offers include an "alliance only" flag -- or better yet, a drop-down box describing the "minimum friendship level" needed to make this trade visible. (Think of it as ordering one's merchants to refuse trade offers from certain parties.) Such a list could consist of ['All','Neutral','NAP','Close Allies','My Alliance'] or something similar -- a lot like what you'd see on the world map anyway.
Additionally, an optional field for comments on the trade might be useful -- a note to go with it, as it were. I realize, however, that this might be asking for a lot of trouble and headache, so consider it merely a thought. The filter/flag combination would be far more useful, and would add another dimension to the diplomatic game.