Hi Mike,
On SyMon, note that it will only emulate 6502, not 65c02, and once you have had those extra commands like BRA at your disposal, you'll never want to give them up. This is the reason I switched to py65. Note I have a Mac, so my options are more limited.
Let me second BigEd here with recommending Python. I mentioned this in a different thread already, but maybe a bit more detail: The core language is laughably easy to learn, which leads to slogans such as "Python fits your brain" or "it's executable pseudocode". No braces, no semicolons, and very clean syntax. For example, to print words from a list each to a line, you have:
Code:
btvs = ["buffy", "willow", "xander", "giles"]
for n in btvs:
print n
That "for w in btvs" is the whole loop. After doing this for a while, every other loop construction seems encrusted with stupid boilerplate. Oh, and you don't have to go around defining "main" functions and whatnot just to get the thing to work (though if you do bigger projects, you'll want to).
The main drawback of Python apart from the missing GUI -- and this drives some people crazy -- is that whitespace is significant. You need those four spaces before the print instruction to signal it's part of the for loop. Get your indents wrong, and things blow up in your face, and are a serious pain to debug. If I remember correctly, it is why Google Go doesn't use whitespace, though a lot of other stuff was influenced by Python.
The language then scales up with more complex constructs. At some point I was lacking the basic concepts (factory functions, etc) to follow the level of abstraction, because I don't have the background of programming theory. It's more than a toy language, though it seems to start out that way.