Let me start off by giving you a little information about the geography of the island so that the rest of what I have to say makes a little bit more sense. It is located in the extreme southern tip of Texas within the Rio Grande Valley, close to Brownsville, Harlingen, and the Mexican border. The island is connected to the mainland by a mile-long bridge that crosses the bay from the small town of Port Isabel, and while the island maxes out to be about a mile in width, it spans north-to-south for many miles up the Texas coast. Only about 5 miles of the southernmost part of the island is accessible by road to the average tourist, but one can see the entire island if he/she has a vehicle with four-wheel drive. Within these few miles, only the southernmost two or three are commercialized, so you will not need four-wheel drive if you look to experience the beach without the crowds.
Although this is not the case all times of the year (see my journal regarding the island during Spring Break), the typical crowd that comes out to the island during the summer are families on vacation. Therefore, activities and festivities on the island are geared for all ages. In addition to the good old-fashioned beach, there is bay fishing, deep-sea fishing, jeep rentals, parasailing, jet-ski rentals, a water park, and dolphin-watch tours (just to name a few things to do). As far as accommodations go, most people elect to either stay in a hotel/resort (there are plenty to choose from) or rent a condo. However, the island is also RV-friendly with a giant RV park at the southern end of the commercialized section. If you're really into the great outdoors, there is always the option of pitching a tent along the beach in the accessible areas north of the developed part of the island. You'll also have plenty of choices with food (I have some recommendations I will talk about later) with everything from upscale restaurants to budget fast-food.
Quick Tips:
There are plenty of good deals at South Padre. I cannot even begin to list everything. My suggestion would be to go to http://www.google.com and type in South Padre Island. All sorts of websites will pop up with additional information and special internet deals.
If I fly down to the area (sometimes I drive), I usually take Southwest Airlines into Harlingen. Their fares are usually comparatively low. However, other good deals exist too. I use a program called Sidestep (http://www.sidestep.com) to find cheap airfare. Since I am also a student, I check http://www.studentuniverse.com and http://www.statravel.com.
Best Way To Get Around:
The best way to get around is by car. I do not even know if the island has public transportation. It is even better if your vehicle has four-wheel drive because then you can drive beyond the point where the road ends into uninhabited beach areas. However, if you stay in a hotel, it is not always necessary to have a car in order to go get a bite to eat, go shopping, or get to either the beach or the bay. The island is not very wide, and there are plenty of shops and restaurants within walking distance of most hotels.