A first glance, getting a monitor for your Amiga seems rather confusing. Can you use a PC monitor? What's the difference between these 15 kHz 'TV' monitors, and multisync monitors? Is it really better than a TV? What's the largest screenmode AGA can display on a monitor? Can you view 640x512 without interlace flicker? Hopefully this article should answer these many questions.
The first thing you should understand is that their are two sorts of screenmodes, 15kHz and 30kHz (Actually, the modes have slightly differing scan rates, but they fall around one of those two). 15kHz can be displayed happily on a TV, and are basically the familiar Lowres, Hires and Super-Hires (with or without Interlace). The 30kHz modes offer much better modes, including DblPAL and Productivity, allowing higher resolutions without resorting to Interlace.
As I said, a TV can only display the 15kHz modes; monitors can be grouped into 3 categories:
I will now consider these in turn...
TV Monitors. These won't offer you any new screen modes. Bear in mind that most games and some applications only run in 15kHz. I will explain this further down, but basically, a VGA monitor that can't display 15kHz modes will have problems, so at least these 15kHz monitors will be completely compatible with your existing setup and programs. All the older Amiga monitors tend to be of this type.
You will still have to put up with interlaced to get a decent resolution (ie, 640x512), but bear in mind that the picture quality should at least be better than what you'd get from a TV. You should be able to get one for under £200 easily. Whether it is worth it is of course up to you; probably not if you have already got a TV to use, but if you haven't, these are worth a look.
PC VGA Monitors. I say 'PC' because I don't know of any 30kHz only monitors which are sold as 'Amiga' monitors. That's probably because 30kHz only isn't recommended. Here's where the problem: Workbench and all modern applications let you select the screen mode, so you can choose one to suit the needs of your monitor. But older applications don't. There are programs (eg, ModePro) which can force a program to run in a particular mode, but anything that isn't OS friendly, in particular virtually all games, will only run in a 15kHz mode. Even the early startup menu (holding down both mouse buttons) is a 15kHz mode, so all these just won't work on PC monitor.
There are other problems, related to the fact that these aren't made for the Amiga. Firstly, the connection is different - the Amiga has a 23pin Video output, so you need a connector (costs about £10). Secondly, a PC monitor isn't guarunteed to run on an Amiga. Using the VGA monitor icon can help, but even if one monitor is found to work, another of the same model may fail, so it is important to test it out before you buy.
If you can live without games and applications that don't run under the OS (and remember that most games coming out now do), and can try the monitor out before you buy, then it might be worthwhile. But for most Amiga users, a multisync would be the best buy...
Multisync Monitors. A proper Amiga multisync monitor, such as one from Microvitec, is undoubtably the best choice. All Amiga modes can be accessed without hassle, that's both the 15kHz TV modes, and all the 30kHz ones too. You'll be able to run applications in 640x512 without interlace (and much more with a graphics card), and still be able to play a game of Settlers without worrying.
Graphics cards.
This is where things get a bit more complicated - and I'm hardly an expert considering that I don't own one. What I do know is that the modes gfx cards output are fully compatible with PC VGA monitors, and the video output connection is what a VGA monitor connects to, so you don't need an adaptor either. So if you are only using the graphics card, a PC VGA monitor will be fine. But...
Again we have the problem that there are programs which won't run on a graphics cards - those same programs which only run in 15kHz, usually. If AGA is being used, you need a monitor switcher/pass-through (standard in the Picasso|V), but of course, you need to have a multisync monitor to view these modes.
Future Proofness.
Will a monitor you buy now be useable in the future? Regarding multisync monitors, the answer is generally yes, but there are small points to consider. If you go out and buy an A1200T with graphics card, the output is VGA style 25pin, so if you have a monitor with a 23pin connector, you need an adaptor to go the other way around! (About £15 - Blittersoft). PC VGA monitors will become more 'useable' as more games support the OS, and running old software becomes less desirable anyway (but you might still like a multisync for video work). TV monitors as far as I know won't work with graphics cards (or if they do, will waste most of its power!) - you certainly won't be able to do more than Hires Laced PAL with one.
Mark