I have found that Grippli are a real hit with female gamers in my local group, especially if you treat them as being evolved from jungle tree frogs as they were illustrated in the issue of Dragon magazine where their 3.5 stats appeared. While bullywugs and other frogmen are more common in fantasy, they tend to be squat, toadlike, and drab in color. Grippli however have bright, cheerful colored patterns, that clearly mark them as individuals with similar color combinations indicating clan or tribe. It may not seem like a big deal, but it gives them a visual "hook" which helps distinguish them from the "drab dryskins". They're small, agile, stealthy, and clannish, just like 4e's halflings, and as frogs they need to stay near some source of water to keep themselves moist, so riverboats are a good habitat for them. They are also incredibly "cute" with their large eyes and bright colors, which allows them to either ingratiate themselves to the locals or divert suspicion away from their larcenous activities. Oh, they also make good thieves, since they literally have sticky fingers
Here is some art to inspire ideas:
http://ursulav.deviantart.com/art/Frog-Tribe-18069793
http://ursulav.deviantart.com/art/Kachina-Frog-471986
My second suggestion is that you use the Nezumi from Rokugan/Oriental Adventures as a base. They are a race of survivors and scavengers who live on the edge of human soceity, relying upon strong familial bonds and determination, skill, and sheer tenacity to survive. They tend to be less disciplined than other races, focusing more on the survival of the group (which often means the adventuring party) over their own concerns. They tend to be rogues, rangers, barbarians or sorcerors, as their short lives and tendency to live in the moment discourages rigorous study or training in anything except the most practical skills. In fact, their religion states that Tomorrow, the personification of the uncertainty of the future and the inevitability of death, is actively chasing their race. Each nezumi is effectively racing against Tomorrow to accomplish all that he can for himself and others before he is caught. This makes Nezumi characters driven and courageous heroes with little concern for pomp and circumstance, and a focus on practicality, tangible rewards, and direct action for the benefit of the greater good.
The only obstacle with the Nezumi is that they happen to be anthropomorphic rats and mice, which is often an archetypal "villain" race (such as the Skaven of Warhammer). However, if you balance the evil Nezumi with good ones (drawing from Rokugan, Red Wall, and various anime that feature mouse-people in a good light) then they have as much breadth of moral standing as any fantasy race. Of course, many people will not look kindly on "river rats", but that works fine for the halfling's niche.
Robert "Frogs and Rats, Rafting Together" Ranting