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Hi J,
what do you want to use the lenses for?
The 18-55 and the tele-zooms you ask about are useless for astro-photography - they just don't have the speed (aperture), low distortion, lack of chromatic aberation etc that you need.
The 20D is a far better camera than the lenses are...
On the other hand, if they are for holiday and family snapshots, then they are fine - probably better than any of the ones I list below due to their smaller size and weight.
If you want something for astro and are on a tight budget, then I'd say go for the 50 f1.8 like Doug said and also a longer fixed tele like 100 or 135 mm.
Otherwise, if you really want a zoom, then the Canon 70 - 200 L f4 is hard to beat - only the 70 - 200 L f2.8 is any better. The f4 version has a rrp of about $1300, but if you shop around, you can get them for about $600 - $650. Apart from the smaller aperture, this lens will equal or outperform almost any fixed lens (eg 100 mm f2) and certainly any of the zooms that you mention.
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