Once any bugs are resolved, I'd also like to see:
1) The AI offer their highest offer right off the bat; I shouldn't have to fiddle with +/- to see how high they'll go (yeah, I know I don't "have to", but I can't help squeezing them if I can without any penalties).
That, or... turn it into more of a fun bluffing game. You only get so many counter offers (depending on their attitude towards you) before they're insulted or done bargaining with you and they cancel it for a number of turns. This way, there's more risk involved and you have to be careful if you wish to make counter offers with them. Also, sometimes the AI will offer you much lower than they're willing to pay.
I think I'd prefer the simplicity of the former one. Plus, the latter can probably still be gamed once you figure it all out.
2) When pressing the left and right arrows to change gold amounts, have holding Shift change the amount by 10 and holding Ctrl changes the amount by 100. I know I can type it, but I'd prefer to just keep my hand on the mouse and click, click, click.
3) The AI stop offering open borders within their deals! I always have to erase it and then fiddle with the amounts until the AI is happy with the new offer. When I'm interested in having open borders, THEN I'll edit the offers and include it. Until then, keep it off the table; unless the AI really is interested in it and needs it (for example, to help get to another civ they're warring with). Actually... that still has nothing to do with their side of the table, they should still keep their own open borders off it. Again, I'll add it in if I'm interested.