Peter I highly recommend the Sandisk range.
Go for at least the Extreme III but the Extreme IV is even better.
For astro the Extreme III is fine.
I highly recommend these guys:
http://www.d-d-photographics.com.au/memory.htm
4GB Extreme III for around $99.
Check out the rest of the range as well.
I buy from them all the time, very happy with the service.
