If you are thinking of changing ISP, and if your telephone is still with "BT" for wires (ie not been local-loop-unbundled) then switching ISP
should be relatively simple.
I've changed three times over the years: the first was a nightmare, the second and third relatively straightforward, although Pipex tried to charge me for another six months after I'd left them. A formal complaint to their MD with a promise that the next would be to somewhere else sorted that.
There are several websites that offer customer feedback on how well the various ISPs perform. Tiscali tend to be towards the bottom of the scale with some good reports, some bad.
I used to use
DSLZone but their website seems to be unmanned, and the number of reports hasn't changed much of late. I think
Thinkbroadband.com is the main one these days.
Some ISPs do indeed offer a free modem/router/whatever, but they then tie you into a 12 or 18-month contract. I prefer a "quick getout" option and to buy my own device.
You can pick up a Netgear DG834 wireless modem router for around £30 on eBay.