decoding the IR-series mosfet numbers: (based on info at fairchild)

prefix IR gate level L (logic level) F (higher level) packaging (default to-220) 5xx 6xx 7xx 8xx w - to-263 s - to-220f i - to-262 nl - to-92l 1xx 2xx 3xx 4xx m - sot-223 p - to-3p r - to-252 s - to-3pf u - to-251 first digit is voltage: 1xx - 100V 5xx - 100V 2xx - 200V 6xx - 200V 3xx - 400V 7xx - 400V 4xx - 500V 8xx - 500V second digit is wattage (goes up, but not the same across lines)

A suitable mosfet for direct connection to PIC/AVR is the IRL510. In general, you need a logic-level mosfet to interface directly to a micro.