Sony Trinitrons are great televisions for earlier game consoles and the Nintendo Wii (I'd hook this and my Xbox up to my HDTV if it had a better scaling chip, but like many, it stinks even when it doesn't have to deinterlace games). I keep my Trinitron hooked up for all my gaming needs except the Dreamcast (Hooked up to a nice computer monitor with a VGA box) and the 360 and PS3 on my HDTV.
But if you're so bent on combating input lag that you'd be considering purchasing a used CRT, I'm confused why you'd be going for an interlaced set? I see several Sony Trinitrons on my local Craigslist for good prices that are progressive scan sets and a couple of HD Trinitron CRT's. And I'm out in a rural area with the highest unemployment rate in New York State outside of the NYC region. So if high end tv's that sold for thousands of dollars in recent memory are widely available here, I'm sure Trinitrons are plentiful everywhere from 480i up to the HD beast they made. A 480p or better Trinitron would give you a better picture than 480i without adding any input lag into the experience.
No reason to specifically seek out a 480i CRT for the 360 unless you wanted one primarily for things like Playstation 2 gaming and earlier consoles (There were some progressive scan PS2 games and a couple of HD games, but the vast majority were 480i or lower, unlike on the Xbox and GCN where a large percentage of releases were progressive scan capable). Or if you have something like a Laserdisc, VHS, or CED collection that you still want to enjoy. Probably not many CED collectors out there (Although I own a player and several releases), but I bet there's a decent number of Laserdisc collectors still around and people with some copy protected VHS tapes that they're hanging on to and can't easily transfer to DVD.
If you do go with a 480i Trinitron, make sure you still hook it up via component. The 360's composite output for some reason stunk compared to something like the original Xbox. When I first bought my 360 a year after launch, I didn't have a HD set and didn't feel like getting in back of my Trinitron since I just wanted to play, so I hooked it up via the front composite input and was shocked at how poor the system's composite out was. But it looked pretty nice when I hooked it up via the component inputs on the rear.
Component gives you a nice boost over s-video at 480i, even though some people seem to be under the impression that its only benefit was for progressive scan or HD output.