Some of these have already been listed, but I am reiterating/adding to the concepts. Please add any of them to the big list that you see fit. Thanks!
1.) A phase correlation meter/goniometer. It's currently impossible to tell if your mix is out of phase without a 3rd party plugin.
2.) The ability to color sections of the arrange view's locator bar in order to visually mark song structure changes.
3.) More flexible navigation of the arrange window. A simple click-and-drag anywhere feature (without having to push additional keyboard buttons).
4.) Quicker, more intuitive vertical/horizontal zoom options. (alt-scroll wheel, ctrl-alt scroll wheel, etc.)
5.) A "No Output" option for track I/O's. (useful for creating a sidechain trigger track with no actual output, among other things.)
6.) A more aesthetically pleasing GUI (3D, more color options, etc). Less Windows '98 looking please, it kills a lot of creative motivation for me upon staring at it for hours on end.
7.) Improved multiple take comps. I like the way Logic did it; if you hit record and loop a section, every subsequent take goes into a sub section of that track. You can then preview all the takes and select pieces from any single one of them to combine into a perfect take.
8.) An easier way to record live performance into Live. Sometimes I will do little remixes of my own song by playing MIDI triggered locators within the song structure. A very simple way to record these actions and/or convert them to clips for quick on the fly remixing/impromptu composition would be amazing.
9.) MP3 export option! WTF!?! (Also as many other formats as you can possibly think of.) Multiple format options simultaneously as well, like bouncing a WAV and a MP3 at the same time would be nice.
10.) An indicator that tells you what note/chord you're playing on a keyboard. Logic had something like this, and it was great for defining non-traditional chord structures on the fly.
11.) Multi-core processor indicator showing the individual cores' processor load. And perhaps an easy way to allocate the specific core's resources to certain tasks in Live.
12.) Border windows around plugins that allow access to certain features of the plugin. (Signal routing, copy/paste current settings, etc.)
13.) Drag and drop information from one instance of Live to another. (clips, tracks, instruments, etc.)
14.) Cleaner arrange window tracks. The current recorded tracks all bump up next to each other and share a common background. It is very confusing to the eyes when you start to get a lot of tracks. Separate them a little more. (Perhaps a more 3D UI could aid in this as well.) Frankly, there's just way too many similar looking lines going on right now.
15.) 64-bit. Obviously. This one hardly needs mentioning. But my extra RAM is getting impatient...
16.) The EQ's should have a spectrum analyzer built in them so you don't have to use two separate plugins.
17.) Sampler should be able to automatically import multiple samples into contiguous zones that are pitch shifted according to the key they fall on but are not
This is all I can think of at the moment, I'll probably think of 5 more as soon as I submit this.