Winter temperatures in Alaska are so low you could fast-freeze a bucket of tossed water midair. But in summer the 49th state sizzles--meaning it's hot, hot, hot for cruises. In fact, the annual gold rush is on: Savvy travelers looking to lock in their first choice for either the best or the cheapest cabins begin booking around now for the narrow vacation season that runs from the end of May through September.

This year, more than 30 vessels will ply the Inside Passage and Gulf of Alaska routes. Every major line is represented, as well as several lines you've probably never heard of. There's a ship in the Last Frontier for you, whether your tastes run to gawking at glaciers, panning for gold, salivating over just-caught salmon or active endeavors such as kayaking, river-rafting, dog-sledding or a climb up Mt. McKinley.

Here's a sampling from this year's Alaska roster:

Of the biggest players, Princess and Holland America will sail seven vessels each--including Princess' two new sister ships, Coral and Island. The 113,000-ton, 2,670-passenger Diamond and Sapphire Princesses will be the largest cruise ships to sail in Alaska. Holland America's fleet will include the 1,848-passenger Oosterdam, the line's first Vista-class vessel in the 49th state. For families, Holland America also has exclusive "Just for Kids" shore excursions. On Crystal's Harmony, which sails 10 12-day cruises from San Francisco, kids can sail free.

Some vessels new to Alaska include Superstar Leo, a 2,000-passenger ship built in 1999 by Star Cruises, Norwegian Cruise Line's parent company, which sails this summer as part of Norwegian's fleet. The vessel, which has seven restaurants, was the first built for Freestyle Cruising, which lets you dine whenever, wherever and with whomever you want. Up a few notches, ultra-luxe Silversea introduces its first Alaska season with the 382-passenger Silver Shadow.

For some sailings, Carnival and Princess have introduced Whittier as an embarkation point for southbound seven-day Gulf of Alaska cruises. Previously, southbound cruises typically departed from Seward, about a three-hour bus trek from the Anchorage airport. The change cuts the transfer distance in half, shaving about 90 minutes of travel time.

No Alaska cruise comes cheap. As a rule of thumb, mass-market lines offer the less-expensive alternatives but sail huge ships that tack on costly shore excursions. By contrast, tiny vessels afford a more intimate, casual and adventurous experience with an up-close focus on nature--some even include excursions--but the cost of these cruises is higher. Keep in mind that small ships also are more likely to offer a truer "Inside Passage" itinerary, which, in the case of some megaships, can be something of a misnomer. As a result of their girth, big ships can't always hug the narrow channels, so they sail "outside" the Inside Passage for part of their route.

In my opinion, nothing beats a small vessel for those with an adventuresome bent. Small vessels focus on destination and discovery, often with naturalists along for the ride, and they rely on Zodiacs and kayaks for exploration. The crew might improvise, perhaps fine-tuning an itinerary depending on the weather and the interests and abilities of passengers, stopping to watch whales or adding more zip to outings.

Even if crowds on small ships tend to be older, they also are inclined to be active and interesting. Small ships swap glitz, casinos, spas and formal nights for a cordial onboard atmosphere. Plus, there's always open seating at mealtimes to promote camaraderie, although dinner choices might run the gamut from blue-plate specials to gourmet surprises.

Here are some lesser-known small lines in Alaska you may want to consider (for rates and more information, contact the cruise line):

- Bluewater Adventures is a 30-year-old company that promises whale sightings every day. "It's completely different, watching wildlife from seven stories up on a cruise ship and watching them from water level," says owner Randy Burke. "When you are floating by, it's so quiet, so peaceful, you can actually hear the animals breathing." Bluewater sails the 12-passenger Snow Goose, a 65-foot steel-hulled research vessel originally a private yacht for Alaska's wealthy. 888-877-1770; bluewateradventures.ca

- British Columbia-based Maple Leaf Adventures offers all-inclusive natural- and cultural-history sailings that passengers describe as "transformational." The sardine of the Alaska fleet, Maple Leaf's five-sailed, no-frills former herring schooner carries just nine passengers. Port calls allow passengers to delve into cultures such as Haida, Kitasoo and Kwakwaka'wakw (that's not a typo). 888-599-5323; www.mapleleafadventures.com

- Cruise West's fleet visits almost two-dozen Alaska ports, ranging in size from Anchorage (population 260,000) to Elfin Cove, home to just 32 residents. Its ships carry no more than 102 passengers apiece. This year, the line puts bears front and center on a new full-day excursion to Hyder, timed for optimum bear-viewing and the salmon-spawning season. 800-580-0072; cruisewest.com

- Lindblad Expeditions will mark its 22nd season in Alaska. The distinguished adventure-oriented line sails the nimble 70-passenger sister ships Sea Lion and Sea Bird where "big boats" can't go. 800-397-3348; expeditions.com

- Surely the most unique way to cruise Alaska is on a paddle-wheeler, just like the vessels that once were a main source of transportation there. American West Steamboat Co. introduced its 235-passenger Empress of the North last year, the region's sole paddle-wheeler. A promotion offers two nights free (on an eight-night cruise), plus free air travel between Seattle and Sitka, Alaska. 800-434-1232; empressofthenorth.com