Hay

Types
There are many types of hay available on the market, however, rabbits should only be consuming either alfalfa, a legume hay, when young or grass hays when older. Additionally, if you decide to buy by the bale, make sure the hay is horse quality, not cow quality, because horses have comparable sensitivity to rabbits while cows are more tolerant.

Here are some links for more general information and pictures on various types of hay in addition to the rest of the information already provided in this article.
 * San Diego House Rabbit Society, Types of Hays and Grasses
 * Atascadero Hay & Feed, Hay
 * House Rabbit Society, Linda Sterett-Fogarty, Hay in Your Bunny's Diet - Quality and Quantities for Healthy Digestion

Alfalfa
Alfalfa is a legume hay, not a grass hay. It is high-fiber like grass hay but also contains more protein, energy and calcium. As a result, alfalfa should only be fed to growing young bunnies under the age of 7 months. For the older bunny, constant alfalfa hay consumption can lead to gummy droppings, weight gain, sludge, and cecal pellets not being eaten.

Alfalfa is typically distinguished by their usually brittle stalks with flat green to brown leaves. Hay can vary from dark lime-green to yellow, green, or brown depending on the season.

A crude analysis for alfalfa provided by Atascadero Hay & Feed is the following:
 * Crude Protein min 16.00%
 * Crude Fat min 1.50%
 * Crude Fiber max 32.00%
 * Moisture max 15.00%

Timothy
Timothy hay is the most popular hay fed to rabbits. It looks like a dried fairly wide blade of grass, and its color is a soft green to grey or brown-green. Timothy hay also has "solid cattails" which distinguishes it from Orchard grass which has "broken cattails."

A crude analysis for timothy hay provided by Atascadero Hay & Feed is the following:
 * Crude Protein min 10.00%
 * Crude Fat min 1.50%
 * Crude Fiber max 32.00%
 * Moisture max 15.00%

Oat Hay
The San Diego House Rabbit Society states, "If bun's diet is high in oat hay, the pellets she produces will be larger, lighter in color, and will look like sawdust if crushed. Many bunnies would benefit from eating more oat hay, an excellent preventative for GI Stasis."

A crude analysis for oat hay provided by Atascadero Hay & Feed is the following:
 * Crude Protein min 7.00%
 * Crude Fat min 1.50%
 * Crude Fiber max 32.00%
 * Moisture max 15.00%

Bermuda Grass
A crude analysis for Bermuda grass provided by Atascadero Hay & Feed is the following:
 * Crude Protein min 8.00%
 * Crude Fat min 1.50%
 * Crude Fiber max 32.00%
 * Moisture max 15.00%

Orchard Grass
A crude analysis for orchard grass provided by Atascadero Hay & Feed is the following:
 * Crude Protein min 7.00%
 * Crude Fat min 1.50%
 * Crude Fiber max 32.00%
 * Moisture max 15.00%

Pet Store
Pet stores will carry a variety of hay (i.e. Timothy, orchard grass, alfalfa, etc.). Typically, the amount that can be bought will range from about 24 oz up to 5 pounds. Although it is convenient to buy hay at a local pet store, this is often an expensive option. A 64oz bag will usually last a couple of weeks at ~$8. Additionally, most pet store brands offer lower quality hay that is very hard and stalky. The recommended popular hay brand is Oxbow, although this may be quite expensive since they carry a premium price compared to other commercial brands.

Some brands may offer fruit mixed in the hay -- DO NOT BUY THESE. Fruit is not necessary for a rabbit and contains a lot of sugar. If your rabbit does not seem to be eating his hay (which is a giant problem), cut down on other sources of his diet (i.e. vegetables, pellets, and treats). If he has no source of food but the hay in his living space, he will consume the hay. Only buy bags of hay with only hay in them and no other treats. Dried herbs are acceptable, however. You can feed fresh healthy treats on the side, independent of the hay and easily rationed.

Through the Local HRS Chapter or Rescue
If you live in a location with an HRS chapter or rescue, check and see if they sell boxes, flakes, or bales of hay at a cheap price! Of course, buying a bale yourself will be cheaper, but if you do not have the space to store it, support your local HRS chapter or rescue! They will most likely sell fresh hay at a better rate than the small bags at pet stores. Your bunny will most likely love and wallow in the fresh hay.

Some examples of HRS chapters and rescues that sell hay include the following:
 * San Diego House Rabbit Society, San Diego, CA -- $12 for 10-12lbs of hay
 * House Rabbit Society Headquarters, Richmond, CA -- $5 for a flake (garbage bag full) of hay

Online in Bulk
Some bunny owners like buying their hay online in bulk. Some of these suppliers also ship much fresher hay than the average commercial brand.

The following a list of reputable online retailers in the US:
 * American Pet Diner
 * Bingaling Bunnybox Store
 * BunnyBale
 * BunnyBytes
 * BunnyLuv
 * FarmerDave
 * KMS Hayloft
 * Sierra Valley Pet Hay
 * Sweet Meadow

By the Bale
The cheapest option typically is a bale of hay. One bale, typically ~70-110lbs depending on type, can feed one rabbit for a year. However, this requires space to properly store the hay as it is easily perishable when wet.

How to Store Hay
It is very important to keep hay dry and out of direct sunlight. Dampness will cause mold in the hay, and sunlight may leech out nutrients in the hay over time. The best location to store hay is in a cool indoor location out of direct sunlight.

If you must store hay outside, invest in a waterproof tarp along with some bricks to keep the hay off the ground.

Not Eating Enough Hay
Rabbits need to have most of their diet consist of hay. If your rabbit does not seem to be eating that much, there is a problem.