What do you mean by compatible?
Do you really mean what switches compete with the 2950 series from other vendors?
From the Cisco Product reference guide here are the competive vendors/products:
Hewlett Packard: Procurve 2500/2650
Nortel: BPS 2000/450T/420T
3Com: Superstack 3300/4300/4400/4400SE/4200 Series
Extreme: Summit 24 e2e3
Dell: Powerconnect 3024/3048/3248
Hirshchmann:
Sixnet: