probably more, but what about link like

http://user:passwd@site

that become specialy interresting when you consider that user or passwd could containt space (or quote ?),that URL can contain comment like "a > b ?", that quote aren't mandatory and finally consider that regex could be memory/CPU hog , and if you still feel like using regexes test things like

perl -Mre=debug -e '"  "=~/href\s*=\s*"*([^"\s]+)"*\s*>/gi'
put your URL here    ^^
[download]

you'll have a better idea of what the regex engine do for you. After that may be your regex be the solution ... but I doubt.