I have the A305 and installed the Patriot torqx 128 Gig SSD, Love it.
But to answer your question I believe your A205 uses a Sata HHD (I also Have A tosibia A205-5xxx (Forgot Model Nr and it is SATA). If so most all of the 2.5" should be fine. Since your laptop only has one HDD bay just make sure it is at least large enough to hold operating system plus programs plus xx amount for your files. add 20% to that to determine size. You can take the HDD that you remove and put in a USB external enclosure for external storage.
Just got an email from newegg "Blowout sale on SSDshttp://promotions.newegg.com/NEemail/Apr-0-2010/SSDSale/index-landing.html?nm_mc=EMC-IGNEFL040210&cm_mmc=EMC-IGNEFL040210-_-EMC-040210-Index-_-Header-_-ClickHere