I suspect that 24 ports will be the smallest you'll find - for example, some of these:
http://www.netgear.com/Products/Swit...tSwitches.aspx
I have experience of the FS726TP (with 2 gigabit ports and PoE on 12 ports) and it seems excellent to me.
Edit:
The GS108T (8-port gigabit switch) appears to have an internal PSU.