I hadn't noticed your Mastermind Solver till not long after posting that.. go figure *facepalm*
Ive played a game before where a Fansite made a very very nifty Firefox Add-on. Essentially allowing a user to use the tools while staying on the game page and being minimally invasive. I think I will attempt to implement something similar, using your site as the resource base of the tools (if your OK with that)... with the use of JS, this would eliminate load on your servers as well.
PhP is a nice server-side option, imo. Allows for quick and rapid development of pages and acts as a bridge for programmers that dont wish to delve into the mechanics of C, C++, or C#. Perl.. is dated

. ASP.. is yucky

Oh yes! Two more suggestions:
1. A database backend for the trivia questions in the game. The questions are obviously asked from a list of questions, Ive come across the same questions multiple times and have helped others with questions Ive come across. So I imagine the trivia portion of the game isnt all that large. Allowing users to submit questions & answers would be great (perhaps require admin/mod review? ) then again, user submitted entries may require too much time on your or a mods part reviewing them all..
2. Text parsing. Essentially, allow the user to copy-paste the entirety of the chicken/cow/horse questions and then use some rather simple parsing to fill out the information. I could whip this up for you sometime if you'd like. Promotes laziness, sure, but I noticed that it took me as long to post all the variables in as it would have to open calculator and do it myself
