For me,
its a EF-S 17-55 F2.8 IS USM for general purpose indoor close sniping and outdoors general.
its a EF-S 70-200 F2.8 IS USM for outdoor sniping, but i don't do nature close-up though. Like some bro said, seldom on telephoto unless it's like an object on away which you cannot reach by positioning yourself.
Agreed with other bros, it's about what you want first then decide with the lens that fits your needs. But I also use EOS450D, just too bad on the 1.6x cropping - I made a mistake here on getting the 450D, might be thinking of upgrading the body some time this year, if no budget to upgrade, I can live with it, just need to get a better angle at things
Maybe might try some macro photography instead... hehehe... but that's another thread liao to consult other bros liao.