Flash or Nifty-Fifty?

In anticipation of the holidays I'm trying to decide my next purchase for my DSLR. Extra spending money is tight, so it will have to be one or the other. I have a Canon T1i with a 18mm-55m IS and a 55mm-250mm IS lens.

My goal is to be able to take some good indoor pictures during the holidays (kids opening presents, etc). Which would benefit me the most for indoor shooting, a Yongnuo YN-468 E-TTL external flash or a Canon EF 50mm f/1.8 II lens? Both can be had for about $100 each.

Thanks!

Well, I know nothing about that flash... but the 50mm f1.8 is fantastic. My wife uses it 100% of the time. I have even seen people use a 50mm f1.8 on a 1D body. I do love flash though and indoors in low light I prefer a flash versus using a 50 or 85mm wide open at higher ISOs. Depending on your skill level you'd need to use that flash in "M" mode since I assume it has no ETTL mode. However, I could show you how to set-up that camera/flash in 10 minutes. I can't remember if the T1i has second-curtain flash or not. Hopefully, so... I'd also invest in a cord to use that flash off camera. I wouldn't use a $60 Canon cord with a $100 flash so use something cheaper.

Here's a link to the flash:

http://www.dealextreme.com/details.dx/sku.37534

This one does have an E-TTL mode and the folks over at POTN have decent things to say about them. The only negative issue is that they ship from China, so if you get a bad one you have to pay the shipping $$$ to send it back. for the most part reviews have been good.

Tough one... I really like the 50 1.8. If think I'd lean towards the 50mm and then I'd fabricate a milk jug difuser thing for the pop-up flash. Gary Fong makes something similar but you can make one just as easy.

Thanks... I appreciate the advice!