Without a display with 1200 lines of resolution, your dreams of 1600x1200 looking really sharp aren't going to happen. If you got a 1920x1080 (1080p) display, you could set the resolution to 1920x1080 and then manually resize your excel window to only take up a 4:3 portion of the screen.
You might be able to send 1440x1080 (4:3) to a 1080p display and have it display a 4:3 ratio with bars on the side. I don't know why you'd want to do this vs. just having extra resolution that you may or may not use on the sides.
I have two 1600x1200 displays next to each other for my desktop, so I too am used to 1600x1200 for program usage. Just to try it out, I've sent 1920x1080 to my projector to see how that felt, and I felt like I had a lot of resolution to work with. This was only on a 720p native display though, so it was definitely lacking in clarity. (I was testing out screen size / seating distance for a future 1080p projector purchase.
If you HAVE to have 1200 lines of resolution, then I think you're stuck looking at large computer monitors vs. HDTVs.
For example, Dell's 2709W is 1920x1200 resolution. It doesn't have a tuner, but you'd be able to hook up to it with different sources through HDMI and Component.
There's the Dell 3007/3008 that is 2560x1600 resolution. The 3007 lacks connectivity options, but the 3008 has a full array. I haven't researched this at all for whether it does a good job with them.
Your request is hard to fill since over the 30" size, I don't know of any options for you that are above 1920x1080 resolution. The "computer monitor" selection of products generally runs up to the 24" range and after that, there are fewer and fewer options... with 30" 2560x1600 options being the top end.
After that (32" and larger), the market is all displays aimed at being used for television use rather than computer usage. If they're targeting TV usage, 1080p is the highest current resolution standard, so the displays only go up to 1920x1080 resolution. A lot of TVs in this range are still 1366x768 resolution too, which is even worse for you.
To get a higher resolution display capable of doing more than 1080 lines of resolution, you might be limited to UXGA and WUXGA front projectors. Those are not what you're looking for.
If you want 32" or larger, I think you're stuck with 1920x1080.
If you can get by with 27"-30", then you could get one of these high resolution monitors with enhanced connectivity options. They will not have a tuner, but that may or may not be an issue for you depending on usage.