The easiest thing to do is to go around to different departments at your university and ask professors who are doing research if they are looking for undergrad assistants or know someone who is. I got my research job by just asking my advisor if she knew of any opportunities and she happened to need the help herself.
You can also look online for opportunities in your area. I don't knwo where you are, but I found a list of good opportunities in research on the BU website, even though I don't go there.
Also, it's probably to late for this summer, but there are lots of summer research programs/internships that you can apply to for next summer (start looking in January).
There are probably a couple of threads about this already; you should do a search.