For those of you who already have a website with a guestbook, or have considered it, I wanted to share this find with you: Lazarus Guestbook.
I was using an open-source guestbook on my website known as Advanced Guestbook, but recently I found it getting spammed to no end by bots. The upgrade to Lazarus takes what was already a powerful solution and makes it secure, along with adding some nice administrative features. The author promises an easy upgrade from existing Advanced Guestbook installations, but since I had tinkered with the MySQL database I ended up doing a little work under the hood. Still – very nice. If you would like to see how I have it integrated into my website, drop in for a peek.