i think pretty much any small pleco (bristlenose, rubberlip, clown) would do great or you could even get a fleet of otos....the tiger barbs, from my experience, rarely (if ever) attack algae eaters...and a pleco won't take any crap from them anyhow
I agree with abstract....Tigers when kept in the proper groups will stick solely to themselves and won't bother any type of bottom dweller....Just stay away from long finned/slow fish and you'll be alright.
Otos can be very hit and miss when you first get them. They rely on a colony of bacteria in their gut to actually break down their diet and give them food. If they become too hungry in transit (noticeably in the lfs by a thin belly) then it usually results with the oto digesting its colony of bacteria and as such it can no longer gain nutrition and will appear to msteriously die.
If you do try them again always try and get the fattest one you can get in the LFS