Nifty 50 is a fun lens. My XTi has "hunting" problems with that lens in AIS? focus mode. Cannot remember what it is called right now. But I have to shoot one shot focus using it. Zooms- I started out with a 70-200 f4L and was not happy so I jumped up to the 70-200 f2.8L IS. Now THAT IS A LENS! Oh, one big difference is your selection of filters. Honestly, go with B&W filters. They are made from optical grade glass just like your lenses are. Cheaper filters are made with regular sheet glass. I noticed a jump in quality when I ditched the Tiffens.
I also have found a lot of fun shooting with the 10-22 EF-S lens I just picked up last month. Great lens for a carshow! But be careful, you will wind up shooting everything with it and get a lot of photos of an interesting perspective, and no shots of standard views!
My gear:
XTi with battery grip
18-55 EF-S IS
10-22 EF-S
70-200 EF f2.8 L
50 EF f1.8
580EX II
I find I can do a lot with what I have. Problem is that everything in my bag is HEAVY! The more you buy, the more you want to take everywhere with you.