If I lived in the US i'd go for one of these as they include the T1 WICs and cables.
http://beaglenetworks.com/index.php?route=product/category&path=63
Out of those, i'd avoid the 3512 and 3524. 2960G would be nice, 2950 are fine for L2 studies.
If you're looking for a L3 switch then at a minimum i'd look for a 3550.
I use one connected to a mirrored port on a switch to listen to all traffic for packet capturing, the other connects to an access port for general use.