размер скачиваемого файла

Плохо искали. --proxy-user=user --proxy-passwd=password

Перед закачкой wget показывает размер. Если хочется графический, то KGet, к примеру, тоже показывает.

$ site='kernel.org'
$ port=80
$ URL='/pub/linux/kernel/v2.6/linux-2.6.11.7.tar.bz2'
$ time echo -e "GET $URL HTTP/1.0\n"|nc $site $port|awk '/Content-Length/ {print; exit}'

Content-Length: 37099602

real    0m0.532s
user    0m0.010s
sys     0m0.030s
$ 

> как определить размер скачиваемого файла до начала скачивания?

HEAD http://host.org/file.txt | grep '^Content-Length:'

А ман по wget прочитать???

$ wget --spider http://www2.ati.com/drivers/linux/fglrx_6_8_0-8.12.10-1.i386.rpm
--16:44:24--  http://www2.ati.com/drivers/linux/fglrx_6_8_0-8.12.10-1.i386.rpm
           => `fglrx_6_8_0-8.12.10-1.i386.rpm'
Resolving www2.ati.com... 84.53.142.22, 84.53.142.9
Connecting to www2.ati.com[84.53.142.22]:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 3,779,718 [audio/x-pn-realaudio-plugin]
200 OK

А там есть хоть слово про headers или размер?

 --spider
           When invoked with this option, Wget will behave as a Web spider,
           which means that it will not download the pages, just check that
           they are there.  For example, you can use Wget to check your book-
           marks:

                   wget --spider --force-html -i bookmarks.html

           This feature needs much more work for Wget to get close to the
           functionality of real web spiders.
#------------------------------------------------------------------
Тогда уж лучше man curl, там хоть понятно о чем речь
curl -I
-I/--head
              (HTTP/FTP/FILE) Fetch the HTTP-header only! HTTP-servers feature
              the command HEAD which this uses to get nothing but  the  header
              of  a  document.  When used on a FTP or FILE file, curl displays
              the file size and last modification time only.

              If this option is used twice,  the  second  will  again  disable
              header only.