Watermarking

Hi all,

So it turns out I need to start doing this with my photos. Luckily I haven't had anyone steal anything yet (that I'm aware of...:/). But I believe putting some HUGE watermark on the photo tends to deter the photo thieves that may be lurking out there.

So, if anyone knows how to watermark, OR knows of a great site that won't involve me using Photoshop (something I need to invest in in the near future) will you guys link them up :)

Thanks!