I’ve long been a fan of Fontifier, which lets you create a font from your own handwriting for $9.
I’m even more excited about their new feature, a signature font creator, that lets you write things like “best wishes” in full signature format (rather than printing — who prints these days?). I haven’t done it yet myself, but it’s great if you need to mass produce thank you notes or if you want to “sign” your electronic newsletters.
I’ve been using yourfonts.com as it allows you to make a font with up to 200 characters.