Hi everyone, since I'm quite new to digital photography I'd like to get opinions ....my brother's friend is selling most of his canon equipment, he has offered to sell to me a canon EF 50mm f/2.5 compact macro lens, a canon EF-S 10-22m f/3.5-4.5 lens, a canon EF 100mm USM and a canon 15-85mm IS USM lens (this one he tells me is the most expensive and something he bought very recently) ... I may have money for just one... I guess I'm going with the canon system if I get another lens...I would like to get something that will complement my existing 18-135mm lens w/c should I pick? bear in mind that I'm just a beginner so I have very little knowledge on the subject ...or should I just save my money?