Animal Emergency Clinic on Packard, just east of Carpenter. We have used them in the past, but it's a trek from where we live. We had no complaints about service, though.
Emergency Veterinary Hospital on Jackson, just east of Zeeb. This is the newest place. We've not used them, yet, but stopped in one day for info. They are very nice, and are open 24/7.
And if worse comes to worse, there is always MSU. Bit of a drive, 49 miles for us, but if the problem is big or unusual that's the place to go.