But, if I am using a crop sensor, would I be better off with a 35mm? 40mm? Is one of the Canon mount primes by anyone, Sigma, Tamron, etc... a particularly sweet lense?
If you're on a crop sensor, you could get the Sigma 30mm f/1.4 for around $300-$350 (crop sensor only lens)
Other 'cheap' lenses you could consider: Canon 35mm f/2 for ~$250, Canon 50mm f/1.8 for around ~$100, Canon 50mm f/1.4 for around ~$325
If you wanted to have some fun and not worry too much about boken, you could pick up the Canon 40mm f/2.8 STM pancake for around $120
If $$$ is no object, you can get the Sigma 35mm f/1.4 for around $800 or Canon 35mm f/1.4L (both full frame lens as well)
It really just depends what you like to shoot though...