i'm preferential to the canon 10-22. i think it's the "best" lens you can get. it costs more, but it's far more versatile than any other UWA lens. (i could not live with an 8-16 or 11-16mm lens. i really do appreciate that 20+mm range and use it quite frequently).
if you are going to france and are only carrying one lens, i think a 10-22 would be FAR FAR more useful than an 11-16 or 8-16. 22mm at least gives you an opportunity for normal-wide-angle photos. the 10-22 also focuses very closely and has an impressive magnification ratio. this is important for getting close up details.
now the $600 budget is a bit tight. i would definitely look for a used 10-22. i sold my 10-22 for $650, i believe? maybe $625. i don't remember it was about 18 months ago on craigslist.
if i could not afford the canon i would go for the sigma 10-20 f/4-5.6. it retails for about $500 new, i think. it's cheaper and has better reviews than the 10-20 f/3.5 version.
i would skip the tamron 10-24. this lens does not get reviewed well in comparison to the other lenses. if i were going for a cheap non-canon lens, i'd go with the sigma 10-20 f/4-5.6
as for the sigma 8-16, tokina 11-16 f/2.8, and tokina 12-24 f/4... these are all fine lenses but i do not think they offer the versatility and convenience of a 10-20ish lens. the 8-16 and 11-16 miss the 20+mm range, and the 12-24 misses the 10mm wide end.
also none of them focus as closely or offer as high a magnification as the sigma 10-20 or canon 10-22 (or nikon 10-24, which is what i presently shoot with)
