Since you would require 24 10/100 Tx ports, the Catalyst 2926G would be a good option. It can be used in a small to medium sized network and also supports MLS. It also has 2 gigabit Ethernet uplinks.
However if you would like to scale your network, it is wiser to go in for a 2948G-L3 switch which has 48 10/100 Base T ports, 2 gigabit ethernet uplinks and supports L3 switching.
The Cat 5k and 6k family of switches could be used for large campus networks.
Layer 4 switching allows finer control over the movement of traffic. Eg. the traffic could be controlled based on source and destination port numbers and supports QOS.
Here the packets are forwarded based on both the layer 3 addressing as well as the layer 4 application information and the layer 4 segment headers are examined to determine the port numbers after the layer 3 protocol type is examined.
