If you want to not be noticed and get great pictures, I would avoid the white L lenses. For v good reach on a crop body, value and very good IQ, I would recommend the 70-300 4-5.6 IS. The IS works great and allows use for fast moving subjects and to hand hold it when slower speeds are essential.
For indoors and limited light conditions, the 50mm 1.4 is a great value and you won't believe the wonderful images it will produce for you. You might want to invest in flash such as the 430 EX. with the extra cash. Check out eBay for that.
After that, it is all up to you....and you still save a little cash. If you sell the existing lenses, give a consideration to the excellent 17-40mm L.
Honestly, I have no idea what you're talking about with the 70-300 4-5.6 IS. The IQ is so much lower than pretty much every other lens I own (most expensive being a 24-105, so we're not talking super high end stuff).
I very much regret buying that lens instead of putting the money towards a 200mm L (The black one).
+1 . Look at this review: http://www.the-digital-picture.com/Reviews/Canon-EF-70-300mm-f-4-5.6-IS-USM-Lens-Review.aspx
More than half way down there's a picture of some trees. Compare the IQ of the 70-300 IS to the 70-200L and see the L blow it in terms of resolution. Honestly speaking I was going to buy the 70-300 IS, but after reading this review, I got the 70-300L instead and love it.