Former Republican Rep. Bob Ney and some former congressional and White House aides were also convicted of charges arising from the Abramoff scandal.
Nearly 5,000 trips, costing lobbyists $10 million, were taken in 2005. This was a peak, which fell to 1,846 in 2006, and then further after reforms were put in place.
Lately, the number of privately financed trips offered by corporate interests, lobbyists, universities and foreign governments, including China, have been rising. Trips this year so far total 1,363, at a cost to the hosts of $3.2 million, according to figures collected by LegiStorm, a nonpartisan watchdog group.
There are 100 senators and 435 members of the House.
Jeff Joseph, a spokesman for the Consumer Electronics Association, which represents corporate giants such as Google,Microsoft, Apple, LG and Samsung, said critics of the travel were "shortsighted."
(Read more: The Washington Post and Jeff Bezos' 'to do' list)
Away from the hustle and bustle of Capitol Hill, lawmakers—whose wives often accompany them—have a chance to "talk to our industry about regulatory issues. They can touch and feel the technologies they are going to legislate on," Joseph said.
Ethics advocates argue that such trips let private groups give members of Congress an earful about their policy positions and that many lawmakers may feel indebted after a week of free food, hotels, tours and transportation.
Bill Allison, editorial director of the Sunlight Foundation, a group which advocates government openness, said the best arrangement would be to conduct all lawmaker travel "on the taxpayer's dime."
"It really doesn't accomplish the purpose of a fact-finding mission if the facts are being presented by a group with a specific viewpoint," Allison added.
A 2007 law passed after the Abramoff scandal imposed new disclosure requirements on lobbyists. The Senate and House also adopted new ethics rules that aimed to stop lobbyists from offering free travel to lawmakers and to require pre-approval of any travel by ethics committees.
The duration of trips was capped at seven days for foreign travel and four days for domestic travel. But the rules contained exceptions, allowing educational and charitable groups to finance trips for lawmakers.
Lobbying outfits have taken advantage of those exceptions by creating their own nonprofit groups that are able to offer and pay for trips taken by members of Congress. These tax-exempt groups "are providing exactly the Jack Abramoff-types of international travel that we intended to ban in 2007," said Holman, of the Public Citizen consumer group.
'Friends of Scotland'
Lawmakers have traveled to a variety of locales this year on trips paid for by private groups and foreign governments, with Turkey the top destination so far, followed by Israel, LegiStorm said. Over many years, Israel's Dead Sea and other resort spots have been popular, along with Tel Aviv and Jerusalem, it added.
Despite the bad publicity years ago from the Abramoff-sponsored Scottish travel, four House Republicans and one Democrat—all members of the "Friends of Scotland Congressional Caucus"—are traveling this month in Scotland, at the Scottish government's expense.
Their visit, in the midst of Edinburgh's world-famous international festival, will include meetings with Scottish officials to discuss "business, economics, energy, infrastructure and natural resources," according to the Scottish Affairs Office at the British Embassy in Washington.
The caucus sponsors an annual "Tartan Day" on Capitol Hill.
(Read more: 'The Wolf of Wall Street': Howls from Hollywood)
Also this month, 10 members of the Congressional Black Caucus visited Beijing, Shanghai and Hong Kong on a trip financed by China. Democratic Rep. Marcia Fudge, who heads the caucus, said the trip's purpose was to "increase mutual understanding" between her members and China's government "through an educational and cultural exchange."
More than 60 House Democrats and Republicans, along with some aides, traveled to Israel and the West Bank on two trips organized and financed by the American Israel Education Foundation. It is an arm of AIPAC, a pro-Israel lobby that pushes for U.S. aid to Israel "to ensure that the Jewish state maintains its qualitative edge over its adversaries."
This education foundation is one kind of tax-exempt, nonprofit organization that lobbying outfits can use to ease the impact of the 2007 travel restrictions.
Despite the criticisms, there have been no known allegations of illegal activity related to travel following the 2007 reforms.
Rep. Steny Hoyer, the No. 2 House Democrat, said the Israel visit helped lawmakers "gain a deeper understanding of American interests in a changing Middle East."
A spokesman for House Majority Leader Eric Cantor, who was on the Republicans' trip, said meetings were set with Israeli and Palestinian leaders, and the visiting lawmakers would "look at facilities Congress has funded like anti-missile systems."
On a similar trip to Israel by a group of House Republicans in 2011, one attendee, Rep. Kevin Yoder of Kansas, jumped naked into the Sea of Galilee for a night swim.
One Washington-based lobbyist familiar with past AIPAC trips, who asked not to be named, said the elegant King David Hotel had long been a favorite for U.S. lawmakers and that tours of Jerusalem's Old City and the Western Wall were a "must."
But some official work is also done, the lobbyist said, adding, "They always meet with President (Shimon) Peres."
While the two trips this August were primarily for first-term lawmakers, in 2011 the AIPAC group ferried about one-third of all the members of the House to Israel. Records show that these visits can cost around $10,000 per member of Congress.
Lawmakers stress the travel's fact-finding nature. But Holman of the Public Citizen group sees it simply as "influence-peddling, an extension of lobbying away from Capitol Hill."
There also is plenty of taxpayer-financed travel by House and Senate members, which is difficult to track.
LegiStorm said that since 2000, a total of 36,411 privately financed trips cost $83 million. According to 2012 figures, Republicans took 793 trips and Democrats took 604, but their costs were about equal.
August recess is not the only popular travel season. Winter months are likely to generate "junkets to places like Las Vegas,New Orleans and Miami. You don't see many trips to Altoona (Pennsylvania)," Allison said.
One of winter's hot tickets, Allison said, was January's Consumer Electronics Association show in Las Vegas. Thirteen lawmakers, 76 aides, all five Federal Communications Commission commissioners and staffers from other federal agencies attended.