Omnidirectional Antennas

[Dave]

Right now I am currently using a 15dBi omnidirectional antenna with 
Host-AP on redhat 9 with a senao nl-2511 CD Plus EXT2.  I like the 
setup as far as the card and server go, but with the antenna I haven't 
been really impressed with it so far.  As of right now I'm getting 
about 150m when I should be getting at least 300m.  Has anyone found a 
good omnidir antenna for a decent price?
I am getting ready to start my second hot-spot, am looking for a decent 
antenna, with the same setup of card and server.

Dave