One of the coolest little CW/AM transmitters can be found at: http://nmwilliam.tripod.com/el84.html
Although the page doesn't mention it, he is using a 12V filament transformer in reverse for the modulation transformer. I think this probably restricts the bandwidth somewhat since there's a lot of DC across there, but it seems to be okay. I would not use a modern HC49U crystal, but an older FT243 type or the like. This has a good bit of current going through the crystal; if it gets warm the frequency will drift.