Sameer has come up with an easy way to build out query strings to use in your GET requests:
Passing variables with a url is such a frequent thing programmers do that most of you may think this post is unwarranted. We call this method of passing variables as GET, the other being POST. It is one of those things which can be easily done in php. [...] The best way to pass GET variables is to use the http_build_query() function available from php version 5; which takes an array of variables and builds a nice URL encoded string which you can append to a url. And example is shown below.
He includes two code examples - one showing "the old way" of building it out by hand and the other using the http_build_query function. You pass in an array and what to connect them with and it builds out the string, no matter how many arguments there are.