windows 7 - Bulk convert photos to smaller size?

I have about 500 photos - each about 5MB in size. I'd like to bulk convert them to a smaller size, suitable for email and web-hosting.

Tools at my disposal -

• Windows 7


• Powershell 2


• A free tool I don't yet know about

What's the best option?

Update - making this a community wiki - there are so many good options I'm not sure it make sense to mark any single one of them as the answer.

Answer

Check out Irfanview!