Okay, I honestly don't mean this as a smart buttocks answer, but if I had the system you describe, and I wanted to drop some money on something music/audio related, I'd buy myself a season subscription to the symphony. (Subscriptions to a chamber music series, a jazz series, the opera, etc., would be viable alternatives.)
Reason? It's worthwhile to have a standard against which to measure your audio system, and a standard with which to calibrate your ears. And when all is said and done, live music, played by living, breathing musicians, right in front of me, sounds more "authentic" than does recorded music played back on even the best audio system.
So my advice is to spend $50-1500 on a dozen tickets to live musical performances.
Okay, if I were jonesing for some hardware, I'd buy one of those 65" HDTV monitors, whose prices seem to have recently dropped dramatically. To the extent that a system will be used for home theater, a good quality, huge picture is nice to have. And if one is willing to settle for less than a plasma monitor, the cost is no longer truely outrageous.
If your 42" monitor satisfies you, dump the (admittedly, very nice) Denon 3803 and buy amp(s) and preamp. Although, honestly, there's nothing wrong with the 3803.
Yeah, pick up a DVD player. It's an inexpensive upgrade. (No need to spend big money to get a good DVD player.)
Depending on the specifics of your room, spending money on treating the walls, ceiling, floor, etc., might even be worthwhile. Or buying a new piece of furniture on which to sit and enjoy your system.
Seriously, it doesn't sound like you have any urgent need for better hardware. And it's no sin to hold off and refrain from buying for a while. I mean, buy more stuff, if you like. But it sounds like you're probably already in pretty decent shape, equipment-wise.
