Which Lenses to Buy?

Hello there,

I am a keen amateur photographer and wanted to ask your opinion on which lenses I should consider buying for my new DSLR (either EOS 600d or the mysterious 650d that might be released in February…..). I have strong interests in macro photography and general wildlife photography. Ideally I would like to keep my budget as close to £1600 or $2500 for two lenses as I am a student (of course i don't particularly mind buying more expensive lenses second-hand). You seem to be the most knowledgeable reviewer that I have read, so I wanted to ask for your help with this decision, if you are able to give it?

I had previously considered both the Canon 18-135mm lens, but then decided I wanted something with a little more reach and therefore chose the Sigma 18-250mm, although I believe the 18-250mm to be a better lens overall than the 18-135 (better AF etc.) I am not entirely happy, what do I substitute for that extra focal length? - Also, because of my interest in Macro work I wanted this 'first' multipurpose zoom lens to have macro capabilities and am regrettably ready accept that 1:1 ratio will not be possible. Dedicated macro lenses with longer focal lengths are just so expensive!!

I also wanted the possibility of a super-telephoto (quick AF) zoom to photograph birds and wildlife that may be some distance away - the ideal lens seemed to be the Sigma OS 150-500mm as on the 1.6x crop body this 500mm maximum focal length would effectivley become about 645mm. However almost all reviews of this lens are at best mediocre. Will I have to substitute focal length for sharpness and image quality?

My basic question is this:

What multipurpose IS zoom lens (with macro capability) should I buy -> which lens will deliver the fastest AF, best quality and versatility within my price range [i.e. value for money]?

What secondary super-telephoto zoom lens should I buy with a view to photographing wildlife such as birds in flight that will deliver crisp 'nice' compositions within my price range?

Many thanks