Look for two or three switches. 2950's or 2960's. Also 3 to 4 routers. 2600 series are pretty cheap, and lots available on auction sites. If you get a NM-4A/S module for one of the 2600's that would be a bonus. Its a 4 port serial interface and you can then configure one of the routers as a frame-relay switch.
The above should be enough to keep you busy for a while and get to grips with the CCENT course content.
I've heard such "what to get for lab" questions in many other contexts, so I started writing down notes. They're collected in the lab gear section of my web site (www.certskills.com/labgear.aspx). There you'll find info on suggested lab topologies, lists of router and switch models that seem to be reasonable from the tradeoff of used market prices versus being too old to support the later IOS's, and other stuff. There's also links to some blog series about building CCNA labs. The last such CCNA blog series was a couple of years back, but the exam hasn't changed since that time.
The short answer is that for routers, 1720/1721 seems to be a reasonably good router in 2010, given those compromises. They support 12.4T (plenty recent, still some longevity/applicability to CCNP for a while if you go on), and are pretty cheap. Vs 2600 non-XM routers, it's better IOS support (12.3 mainline is the latest 2600 non-XM version, which is basically 2 major versions older than 12.4T). But 2600 non-XM's can be cheap, so they're reasonable, just not as good IOS version support. For example, you don't get IPv6 support in the 2600 non-XMs. The web site is there with all this info cause I would look it up, forget it, look it up again, etc, so I just wrote it all down and try to keep it updated.
2950's are a nice sweet spot for switches again comparing features to used prices, again in my opinion.
Great info on the site Wendell, very useful.
Regarding GNS3 - check the documentation page on the GNS3 site, they have a good starter tutorial that should help to get going. - http://www.gns3.net/documentation.