Lings on creep outspeed reapers unless they have their speed upgrade. If you get ling speed it's no contest.
Right now the hardest thing to fend off is the proxy reaper bunker rush against Protoss.
Basically, they send their first SCV out, build a barracks right next to your base, drop a tech lab, send a reaper in, send that SCV in to build a bunker right next to your nexus, then sit the reaper in the bunker and destroy it. As soon as the reaper is done building, they build a marauder to take out any sort of early stalker you put out.
It's very simple to counter, but you have to execute a 10gate* zealot/stalker opening perfectly, block the bunker, and kill the SCV or you're boned. Good news is that if you do fend it off, you can walk into his completely unguarded base and destroy him.
*Edit: It occured to me this might be confusing to some people, it refers to the amount of probes you have when you build the Gateway, it doesn't mean you build 10 Gateways in your base.
Edit2: Megabytten.megs and I'm gold league (was platinum before) in 1v1 and Plat in 2v2. If you think that bunker reaper rush thing is hard to fend off in 1v1, wait till you see that + 6 zerglings in your base :(