A sniffer is must have for network guy.
A good sniffer need to be
1. Allow filter. (too much noise)
2. Understand OSI model and be able to translate before hands (I am not going back to tcpdump, and you don't want neither)
3. Allow generate report by filter.
4. Be able to read at Gb/seconds speed
5. Free. (I remember first windows sniffer was asking 1000 Pounds per user license back in 1997, where snort are about to born)
6. a Good sniffer should be able to tell you is there a NetCut running in your network
With above 3, I am happy with it. So, here comes list. (if you feel a missing, please let me know