One of my favorite lighting modifiers is my Speedlight beauty dish and it's one of my favorites for several reasons:
1. I love the light it gives me
2. It's very easy to use
3. And it's extremely portable
It also easily customizable, just 2 of pieces of printer paper and 4 clothes pins and you have instant barn doors. Another option is paper + tape = snoot, but be sure to attach it to the beauty dish with gaffers tape (or much less expensive hockey tape) so no sticky residue is left behind.
If you are leaning towards the "buy one" option I have something for your consideration.
Adorama has a 12 inch beauty dish kit that is $84 (with free shipping) and comes with everything you would possibly need.
It includes a mounting bracket that will allow it to fit onto any tripod or light stand, it comes with two center rings - one deflector AND one diffuser, it also comes with a honeycomb grid, and a washable fabric diffuser sock (with a heavy duty elastic band to hold it securely in place).
So you can follow this link and learn how to make your own beauty dish, or follow this link to buy one that will give you just a few more (lighting) possibilities.