Get a submersible filter, so you can adjust the flow. One of those you can keep vertical or horizontal. Like a Fluval 1. I think that the Whisper Internal Micro Filter would be a good choice as well...
Another option is one of those corner filters, or sponge filters. I know breeders use them in fry tanks so the current can't be that big of a problem. And they're cheap as well, just need an airpump and you're all set... Never used either though, so maybe someone who has experience w/ these products can post and tell you how effective they are.
I used to use a Regent Aquatech 5-15 filter on my old 10G, which used to have a betta in it. They don't cost too much in Walmart and they're made by Marineland as well. The thing is you don't need a filter which is rated for a 10G even, you just need a filter that has enough surface area to let enough benefitial bacteria grow.