A lot of people like the 6.6 gallon book shelf tank from petco because it is longer than tall..
walmart also has a 5 gallon starter kit a little more expesnive online, but i think its about $35 in store http://www.walmart.com/ip/Tetra-Aqua...-Pets/12177653
Add tranquility and beauty to any living space with the Tetra Aquarium Starter Kit. This five-gallon aquarium kit includes enrollment in Tetra's free TetraCare program to help you get started. The glass tank includes a hood light and power filter (complete with three-stage filtration) to help your aquarium stay clean. Plus, your Tetra Kit includes starter samples of TertaMin Tropical Flake Food and instructions on how to keep your fish tank extra clean. Welcome your fish family into their new home with AquaSafe water conditioner, so they breathe easy in their new fish tank.
Tetra Aquarium Starter Kit:
- Bio-Bag Filter cartridge
- Three-stage filtration
- Fish net
- AquaSafe water conditioner
- Tank size: 5 gallons
- Glass tank
- Hood with light
- Starter samples of Tetramin Flake Food
- Instructions on water care
- Free enrollment in TetraCare program
Im not sure what kind of heater you have in your tank, but for a 2.5 gal tank you need a 25 watt heater but no more than 50 watts... adjustable with a thermostat.. heres a good one if you need a new heater ;)