If you want some advice from someone who rolls with people who have spent more than my life savings on canon gear, and does ALOT of lens testing and trading, take a listen:
Dude, skip the 20d and at least grab a 30d- they've hit the most significant part of their price drop now that they're not the current model, and they're still otherwise far more current and in better conditions than most of the 20ds you're going to find. 20d is two generations out, and you lose alot of the improvement in interface, extra screensize, better autofocus, etc. etc.
Treat it like an investment; for a couple hundred more you'll get improved pictures, or at least an easier time taking good pictures for as long as you keep it, which'll be longer by average manufacturing lifespan, and an increased value if you ever do decide to resell it.
There's another thing to consider:
Right now, with the 24mm on a crop body, that translates into give or take a 38mm, which won't allow you much flexibility in the way of interior photography or landscapes... you're going to suffer if every time you can't get everything in the shot if you don't have wide-angle.
At bare minimum the cheapo 18-55 kit lens, but if you're using L-glass the rest of the time you'll want to chuck it off a cliff. Probably at least a 10-20 Sigma (equivelant to 15-30mm on crop body) for about $400 if you want decent quality... you could do 17-40 for about $600 if you really need to have L glass, but a 10-22 Canon for about $650 is going to be your best combo...
I'm estimating here, of course, because I do all my trading in CAD and the market here is way different.
Anyway, the other option I was going to say is: skip all the hubub of needing an extra wide-angle lens later on and invest the money you're going to yearn to spend on it in a full-frame like the 5d instead, or wait until the new one is officially released and get an even better deal.... With the L lens, you'll get incomparable image detail and sharpness the 20d OR 30d can't touch, you'll get a true wide angle at 24mm, and most of all you'll be the envy of all your 20d/30d peers.
Barring that, if you're still stuck on the 30d (hopefully you've been listening), sell the 24-105mm f4 IS and grab the 17-55 F2.8 IS... it's not L, but it's sharp as or sharper than the 24-105, a stop faster, a lot wider, and has awesome IS.
Here's my personal inkling, since I've given you so much mutually contradicting advice: If you see the wisdom in my words and are willing to scrimp a bit for the full frame upgrade, plan on playing around with the 20d right now until the 6D is announced, probably at the PMA this winter. Then, snatch up a 5d when all the trendsetters are getting rid of their old toys for the new one...
However, if you want to get a body and stick with it till product death do you part, skip the 20d and go for a 30d, or else get a 5d right now. But there's no sense cheaping out for a measley two hundred on something you're hoping to spend at least a few years with and expand your capabilities with. I speak from experience.
