I would say no, there are no other sub-$250 gems. You can get a lot of really nice lenses in the $350-$550 range, but below that there's nothing really that qualifies as a gem. I was mostly happy with my Tokina 19-35 until I got a Sigma 24-70 f/2.8.
I'd say the Sigma is sharp at f/2.8 except as you get up to 70mm. Good enough for my standards. The Tokina can use some stopping down, usually one stop is enough, but it's reasonably sharp. I've never used L glass though, so I can only compare this to the 50mm f/1.8.