I have a signal output that switchs 0 to 2.5v (100ma). the voltage is
too low to switch a standard relay. Does anyone know of a low voltage
activiated relat or a chip I could use to boost the signal to 5V to
pull the relay?

Radio Shack has a optocoupler triac which has a 2 to 2.5 volt input to
a led that switches a triac on. It comes in a 6 dip ic chip and 
use 4 of the terminals. If the voltage is ac, convert the input to dc 
with diodes but you may want to use germamium diodes because of the
voltage loss with regular diodes .5 volts adc a small cap, maby iuf on
the input. If the switched voltage is dc, then once on, it will not shut
off untill current stops so this only work with ac switching.

Hey, how about this!
Radio Shack has Engineer's mini notebooks with a 1000 different 
applications including diagrams ,operation and the part numbers.

Radio shack use to hace a special 1.5 volt relay, don't think they
have it anymore, but you may be able to order one in their parts catelogue.

Sorry about the spelling , did not check it befor posting!

Build it : http://gifbrothers.com/folder1/diagram001.gif
 Made a circuit that may do the job in the above link,
but you still need a 5 volt supply.
Your on your own by not having a UL approval on this.
good luck!