-should have less power than the speakers
-must have a phono input

Example:
http://www.hifi-forum.de/viewthread-172-8561.html

Generally it seems to me that the offers at hifi-forum are more honest. Search for amps that fit into your category (max. 120 watts R.M.S. Per channel at 4 Ohm & Phono input) and then feed the name of the amp to google. Mostly you'll end up in the hifi-forum were you get the information about the value of the amp.

Edit: Und lass Dich nicht von hohen Wattzahlen verrückt machen. Die Alesis speaker sind an 40 Watt schon verdammt laut.