I've never had shrimp, but usually see them recommended for cleaning algae. I'd go with snails though, just personal preference. Nerites seem a popular one for eating algae.
By cats do you mean corydoras? If so, they are not for cleaning algae. They need a mainly meaty diet which can be provided through shrimp pellets, but some veggie is good for them too.
I don't know how they do with algae eating but have care what tank mates you keep with them. I dropped 30 into my "peaceful community" tank and lost every one of them inside of two weeks. I knew it was taking a chance since I have a rainbow shark, but I didn't expect my neons to nip them. They did.
I got six ghost shrimp a week ago, and still see at least three regularly on the plants doing their business. My Cardinals ignore them and my Betta does too. By cats I meant plecostomas or the algae eater kind, which are kind of aggressive.
Thanks for the responses.
Depending on you stock list and what the quality of your LFS stock is you may be interested in otocinclus catfish. I wouldn't buy them just for algae eating purposes, but they are neat little fish to watch. They can be tricky however and you need to excercise caution when buying them. Glad the shrimp seem to be working out for you. Hopefully your fish continue to leave them alone!