The A650IS is more similar to your previous camera, the Canon A85, than the S5IS. The S5IS is larger, has more optical zoom and has a flash hotshoe. However, the S5IS has a smaller sensor than the A650IS and it's not as good as the A650IS in low light shooting situations.
Canon is going to announce its new cameras very soon and it's expected that there will be a new version of the S5 (the S6IS?), perhaps the A650IS (A660IS?) and the A720IS (A730IS?). If you can wait a little while, it might be worth it to see what Canon has come up with.