Schwinn Admiral 700c 7 speed, fenders, rack $159

$159, the Schwinn Admiral is one of the best value commuter bikes you can get at Walmart.
http://www.walmart.com/ip/700c-Schwinn-Admiral-Women-s-Hybrid-Bike-Powder-Blue/26999382
http://www.walmart.com/ip/700c-Schwinn-Admiral-Hybrid-Men-s-Leisure-Bike-Matte-Red/26999373

The Admiral has a high tensile steel frame and fork.
It has aluminum 700c wheels, that roll fast.
7 speed gripshift and shimano derailleur.
Aluminum linear pull brakes.
Upright sweptback handle bars and a beach cruiser seat.
Steel fenders and rear rack.

 Like most walmart bikes, it only comes in one size.  The men's model fits people 5'6"- 5'10".  The women's model fits 5'2-5'-6".

Walmart does not assemble bikes very well.  The same kid that puts together the BBQ grills, puts together the bikes.  Most bike shops are pretty honest.  Bring the bike to a shop, tell them you will be riding it to work and would like it safe, and they will take care of you for under $50.

One of the best features of the Admiral, are it's good quality, aluminum 700c wheels.  It has an alloy quick release front hub, and solid axle nutted freehweel rear.  700c aluminum rims can fit a wide selection of road, touring, and commuter tires. However, the schwinn tires that come on the bike are very cheap, do not take high pressure, and are prone to flat tires.  The best thing to do to this bike to make it a more reliable commuter is better tires.  Nothing ruins your day like flat tires.

Plan to buy better tires.  Good commuter tires are Continental, Schwalbe, Michelin touring.
These Vittoria 700X32c tire are slightly skinnier than the stock 35c tires.  $30 pair.
This is a great deal on Schwalbe Marathon 700x35c tires.  They are very tough to flat, and very long lasting.
Some of best commuter tires you can get. Blue Sky has them $40 for the pair.

The beach cruiser springer seat is made for cruising, not pedaling.  The springs are heavy and squeaky.  The seat is very wide and rubs on your legs when pedaling.
The seatpost with cheapie seat guts is heavy and prone to slipping and creaking.
I would suggest a better seat for $20-30 and an aluminum seatpost for $15-20.

http://www.blueskycycling.com/product7576_46_-WTB-Freedom-Econoline-Saddle.htm $33

The Avenir Classic has real leather cover, for $30.
http://www.amazon.com/Avenir-Classic-Series-Saddle-Black/dp/B003RLDH0E

Singleworks city limit, leather, $20

Kalloy 2 bolt aluminum seatpost

Seatposts come in many sizes.  It is important to check the size of your post to make sure you get the right size.  Luckily, the size is stamped at the bottom of the post.  Remove your post and look for marking:

This example, not the Schwinn, is stamped 26.8.   Post sizes are diameter X length.  This example post is 26.8mm.  Common length is 350mm or 35cm.  400mm is long.  250-300mm is short.  You can always cut a long post down.  Common diameters are 25.4, 26.0, 27.2, etc.  Make sure you get the right size!
Amazon is a good place to buy a post.  Search "kalloy" and "27.2" or "25.4" or whatever the correct size is.

The admiral uses a aluminum quill stem.
It's steel handle bars are swept back. They give you an upright, comfortable position.  Good for short trips.  If you are riding longer distance, lower, less swept back bars would put you in better position to cut through the wind.  The steel bars are quite heavy, and aluminum bar saves a lot of weight.
http://store.velo-orange.com/index.php/components/handlebars/vo-milano-handlebar-22-2-dia.html
It uses a gripshift 7 speed shifter, good quality.
Aluminum V-brake levers, also decent quality.
The brake and shift cables and housing are poor quality.  The cheap housings flex a lot, makes your brakes feel mushy and shifting vague.  Jagwire, Shimano, Sram make quality cables & housing that will drastically improve shifting and braking of the bike.
Brake cables & housing, $13

The aluminum V-brakes are functional, but not great quality.  The stock brake pads are very hard plastic-y compound.  The brakes themselves have play on the bosses and cheap plastic spring adjustment.  I would suggest upgrading to Shimano Acera brakes fore $14.  Not much more than $8 brake pads.

The drive train is basic, durable, and replacement parts are inexpensive.  The drivetrain is the crank and chainring, the chain, and the freewheel.  Drivetrains typically last around 3000 miles.  That sounds like a lot, but if you are riding 5 miles to work each way, that 10 miles a day, 300 days.  Tires, brake pads, and drivetrains are consumables.

It uses a steel one piece crank and steel sprocket.  This is heavy and crude, in comparison to three piece aluminum cranks that come on bike shop quality bikes, but it gets the job done, and is durable.  This style of crank is common on beach cruisers and kid's bikes.

The 7 speed freewheel costs $12 to replace with good quality shimano one.
Better quality SRAM chain is $8.
This bike has one of the most affordable drivetrains to replace.  The steel chainring, while heavy, is durable.
The Shimano Tourney derailleur is basic, and replacements are about $14.