You really should have a metronome you know ;)

Or at the last use an online one.

Anyway, one of the Boss Loopers should do you fine, they are available in various versions depending on requirements, how many layers you want to record etc.

Boss RC-3 Loop Station, 3 Hours of Stereo Recording in a Compact Loop Pedal[br]Stocked with a number of powerful features somehow packed into a compact pedal, the Boss RC-3 Loop Station is an incredibly useful loop pedal.

USB 2.0 compatibility, three hours of stereo recording time for up to 99 loops and a “real drums” rhythm guide and suitable for guitar and bass – the Boss RC-3 Loop Station is one incredible stompbox loop pedal.

Boss RC-3 Loop Station Loop Pedal Key Features:[br]Compact and powerful stereo stompbox looper[br]Massive internal memory with up to three hours of stereo recording time[br]99 onboard memories for storing loops[br]USB 2.0 port allows you to connect to a PC and import/export WAV audio[br]Rhythm guide with real drums[br]Runs on a single 9-volt battery or optional AC power supply[br]BOSS five-year warranty