i have the same basic setup (100mbit router -> gbit switch -> 2 pcs) running for some years now, using the cheapest switch i could get and i dont have any problems with it. the switch is a d-link dgs-1005d wich costs about 22€ here in germany, so about the cheapest you can get. there is not much difference in those cheap switches anyway, they all use the same hardware. the performance is quite good, getting >900mbit effective transfer rates.
Code:
I:\Downloads>iperf.exe -w 128K -t 30 -c 192.168.178.20
------------------------------------------------------------
Client connecting to 192.168.178.20, TCP port 5001
TCP window size: 128 KByte
------------------------------------------------------------
[156] local 192.168.178.30 port 5927 connected with 192.168.178.20 port 5001
[ ID] Interval Transfer Bandwidth
[156] 0.0-30.0 sec 3.18 GBytes 909 Mbits/sec
in your situation i would just buy anything cheap that is available from your store of choice.