You can get the entity type codes on MSDN. (http://msdn.microsoft.com/en-us/library/bb887791.aspx, note this is from CRM 4.0 documentation, but valid for CRM 2011 too)
Another way you can get them is through the CRM database using the following query:
SELECT ObjectTypeCode,Name
FROM
ENTITYVIEW
order BY ObjectTypeCode
The above is the only way to get entity type-codes for custom entities.
1 Account
2 Contact
3 Opportunity
4 Lead
5 Annotation
6 BusinessUnitMap
7 Owner
8 SystemUser
9 Team
10 BusinessUnit
11 PrincipalObjectAccess
12 RolePrivileges
13 SystemUserLicenses
14 SystemUserPrincipals
15 SystemUserRoles
16 AccountLeads
17 ContactInvoices
18 ContactQuotes
19 ContactOrders
20 ServiceContractContacts
21 ProductSalesLiterature
22 ContactLeads
23 TeamMembership
24 LeadCompetitors
25 OpportunityCompetitors
26 CompetitorSalesLiterature
27 LeadProduct
28 RoleTemplatePrivileges
29 Subscription
30 FilterTemplate
31 PrivilegeObjectTypeCodes
32 SalesProcessInstance
33 SubscriptionSyncInfo
35 SubscriptionTrackingDeletedObject
36 ClientUpdate
37 SubscriptionManuallyTrackedObject
40 TeamRoles
41 PrincipalEntityMap
42 SystemUserBusinessUnitEntityMap
43 PrincipalAttributeAccessMap
44 PrincipalObjectAttributeAccess
112 Incident
123 Competitor
126 DocumentIndex
127 KbArticle
129 Subject
132 BusinessUnitNewsArticle
135 ActivityParty
150 UserSettings
1001 ActivityMimeAttachment
1002 Attachment
1003 InternalAddress
1004 CompetitorAddress
1006 CompetitorProduct
1010 Contract
1011 ContractDetail
1013 Discount
1016 KbArticleTemplate
1017 LeadAddress
1019 Organization
1021 OrganizationUI
1022 PriceLevel
1023 Privilege
1024 Product
1025 ProductAssociation
1026 ProductPriceLevel
1028 ProductSubstitute
1030 SystemForm
1031 UserForm
1036 Role
1037 RoleTemplate
1038 SalesLiterature
1039 SavedQuery
1043 StringMap
1055 UoM
1056 UoMSchedule
1070 SalesLiteratureItem
1071 CustomerAddress
1072 SubscriptionClients
1075 StatusMap
1080 DiscountType
1082 KbArticleComment
1083 OpportunityProduct
1084 Quote
1085 QuoteDetail
1086 UserFiscalCalendar
1088 SalesOrder
1089 SalesOrderDetail
1090 Invoice
1091 InvoiceDetail
1111 SavedQueryVisualization
1112 UserQueryVisualization
1113 RibbonTabToCommandMap
1115 RibbonContextGroup
1116 RibbonCommand
1117 RibbonRule
1120 RibbonCustomization
1130 RibbonDiff
1140 ReplicationBacklog
1200 FieldSecurityProfile
1201 FieldPermission
1202 SystemUserProfiles
1203 TeamProfiles
2000 AnnualFiscalCalendar
2001 SemiAnnualFiscalCalendar
2002 QuarterlyFiscalCalendar
2003 MonthlyFiscalCalendar
2004 FixedMonthlyFiscalCalendar
2010 Template
2011 ContractTemplate
2012 UnresolvedAddress
2013 Territory
2020 Queue
2027 License
2029 QueueItem
2500 UserEntityUISettings
2501 UserEntityInstanceData
3000 IntegrationStatus
3231 ConnectionRole
3232 ConnectionRoleAssociation
3233 ConnectionRoleObjectTypeCode
3234 Connection
4000 Equipment
4001 Service
4002 Resource
4003 Calendar
4004 CalendarRule
4005 ResourceGroup
4006 ResourceSpec
4007 ConstraintBasedGroup
4009 Site
4010 ResourceGroupExpansion
4011 InterProcessLock
4023 EmailHash
4101 DisplayStringMap
4102 DisplayString
4110 Notification
4200 ActivityPointer
4201 Appointment
4202 Email
4204 Fax
4206 IncidentResolution
4207 Letter
4208 OpportunityClose
4209 OrderClose
4210 PhoneCall
4211 QuoteClose
4212 Task
4214 ServiceAppointment
4215 Commitment
4230 UserQuery
4250 RecurrenceRule
4251 RecurringAppointmentMaster
4299 EmailSearch
4300 List
4301 ListMember
4400 Campaign
4401 CampaignResponse
4402 CampaignActivity
4403 CampaignItem
4404 CampaignActivityItem
4405 BulkOperationLog
4406 BulkOperation
4410 Import
4411 ImportMap
4412 ImportFile
4413 ImportData
4414 DuplicateRule
4415 DuplicateRecord
4416 DuplicateRuleCondition
4417 ColumnMapping
4418 PickListMapping
4419 LookUpMapping
4420 OwnerMapping
4423 ImportLog
4424 BulkDeleteOperation
4425 BulkDeleteFailure
4426 TransformationMapping
4427 TransformationParameterMapping
4428 ImportEntityMapping
4500 RelationshipRole
4501 RelationshipRoleMap
4502 CustomerRelationship
4503 CustomerOpportunityRole
4567 Audit
4600 EntityMap
4601 AttributeMap
4602 PluginType
4603 PluginTypeStatistic
4605 PluginAssembly
4606 SdkMessage
4607 SdkMessageFilter
4608 SdkMessageProcessingStep
4609 SdkMessageRequest
4610 SdkMessageResponse
4611 SdkMessageResponseField
4613 SdkMessagePair
4614 SdkMessageRequestField
4615 SdkMessageProcessingStepImage
4616 SdkMessageProcessingStepSecureConfig
4618 ServiceEndpoint
4700 AsyncOperation
4702 WorkflowWaitSubscription
4703 Workflow
4704 WorkflowDependency
4705 IsvConfig
4706 WorkflowLog
4707 ApplicationFile
4708 OrganizationStatistic
4709 SiteMap
4710 ProcessSession
4800 WebWizard
4802 WizardPage
4803 WizardAccessPrivilege
4810 TimeZoneDefinition
4811 TimeZoneRule
4812 TimeZoneLocalizedName
7100 Solution
7101 Publisher
7102 PublisherAddress
7103 SolutionComponent
7105 Dependency
7106 DependencyNode
7107 InvalidDependency
8000 Post
8001 PostRole
8002 PostRegarding
8003 PostFollow
8005 PostComment
8006 PostLike
9100 Report
9101 ReportEntity
9102 ReportCategory
9103 ReportVisibility
9104 ReportLink
9105 TransactionCurrency
9106 MailMergeTemplate
9107 ImportJob
9333 WebResource
9502 SharePointSite
9508 SharePointDocumentLocation
9600 Goal
9602 GoalRollupQuery
9603 Metric
9604 RollupField